Display device and method for manufacturing the display device

ABSTRACT

The manufacturing yield of a display device is improved. The resistance of a display device to ESD is increased. The display device includes a substrate, a display portion, a connection terminal, a first wiring, and a second wiring. The first wiring is electrically connected to the connection terminal and includes a portion positioned between the connection terminal and the display portion. The second wiring is electrically connected to the connection terminal, is positioned between the connection terminal and an end portion of the substrate, and includes a portion in which a side surface is exposed at an end portion of the substrate. The display portion includes a transistor. The transistor includes a semiconductor layer, a gate insulating layer, and a gate electrode. The semiconductor layer and the second wiring include a metal oxide.

TECHNICAL FIELD

One embodiment of the present invention relates to a display device. Oneembodiment of the present invention relates to a method formanufacturing a display device.

Note that one embodiment of the present invention is not limited to theabove technical field. Examples of the technical field of one embodimentof the present invention disclosed in this specification and the likeinclude a semiconductor device, a display device, a light-emittingdevice, a power storage device, a memory device, an electronic device, alighting device, an input device, an input/output device, a drivingmethod thereof, and a manufacturing method thereof. A semiconductordevice generally means a device that can function by utilizingsemiconductor characteristics.

BACKGROUND ART

Display devices using organic EL (Electro Luminescence) elements orliquid crystal elements have been known. Other examples of the displaydevice include a light-emitting device provided with a light-emittingelement such as a light-emitting diode (LED), and electronic paperperforming display with an electrophoretic method or the like.

As a semiconductor material applicable to a transistor included in apixel in a display device, an oxide semiconductor using a metal oxidehas attracted attention. For example, Patent Document 1 discloses asemiconductor device that makes field-effect mobility (simply referredto as mobility or μFE in some cases) to be increased by stacking aplurality of oxide semiconductor layers, containing indium and galliumin an oxide semiconductor layer serving as a channel in the plurality ofoxide semiconductor layers, and making the proportion of indium higherthan the proportion of gallium.

A metal oxide that can be used for a semiconductor layer can be formedby a sputtering method or the like, and thus can be used for asemiconductor layer of a transistor included in a large display device.In addition, capital investment can be reduced because part ofproduction equipment for transistors using polycrystalline silicon oramorphous silicon can be retrofitted and utilized. Furthermore, atransistor using a metal oxide has high field-effect mobility comparedto the case of using amorphous silicon; therefore, a high-performancedisplay device provided with a driver circuit can be achieved.

REFERENCE Patent Document

[Patent Document 1] Japanese Published Patent Application No. 2014-7399

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

A transistor, a capacitor, or the like is sometimes broken due toovervoltage caused by electrostatic discharge (ESD) or the like in themanufacturing process of a display device. In particular, in the casewhere a display device is manufactured using an insulating substratesuch as a large glass substrate, electric charge tends to be accumulatedin a wiring or the like, leading to a reduction in yield.

An object of one embodiment of the present invention is to improve themanufacturing yield of a display device. Another object is to increasethe resistance to ESD of a display device. Another object is to providea display device having high reliability. Another object is to provide adisplay device having a novel structure.

Note that the description of these objects does not preclude theexistence of other objects. One embodiment of the present invention doesnot have to achieve all these objects. Note that objects other thanthese can be derived from the description of the specification, thedrawings, the claims, and the like.

Means for Solving the Problems

One embodiment of the present invention is a display device including asubstrate, a display portion, a connection terminal, a first wiring, anda second wiring. The first wiring is electrically connected to theconnection terminal and includes a portion positioned between theconnection terminal and the display portion. The second wiring iselectrically connected to the connection terminal, is positioned betweenthe connection terminal and an end portion of the substrate, andincludes a portion in which a side surface is exposed at an end portionof the substrate. The display portion includes a transistor. Thetransistor includes a semiconductor layer, a gate insulating layer, anda gate electrode. The semiconductor layer and the second wiring includea metal oxide.

In the above, the semiconductor layer and the second wiring arepreferably provided on the same plane and preferably include the samemetal element.

In the above, the semiconductor layer preferably includes a first regionoverlapping with the gate electrode and a second region not overlappingwith the gate electrode. At this time, the second region and the secondwiring preferably have lower resistances than the first region.

In the above, the second wiring preferably has a higher resistance thanthe first wiring.

In the above, a third wiring electrically connected to the transistor ispreferably included. At this time, the third wiring and the first wiringare preferably provided on the same plane and preferably include thesame metal element.

In the above, the connection terminal preferably includes part of thefirst wiring.

In the above, an FPC electrically connected to the connection terminalis preferably included. At this time, the FPC preferably includes aportion overlapping with the second wiring.

In the above, the substrate preferably includes a first portionoverlapping with the first wiring and a second portion overlapping withthe connection terminal and the second wiring. At this time, the firstportion is preferably bent so that the first wiring is on an outer side,and the second portion preferably includes a region overlapping with thefirst wiring or the display portion.

Another embodiment of the present invention is a method formanufacturing a display device including the steps of forming atransistor including a semiconductor layer, a plurality of connectionterminals, and a wiring electrically connecting the plurality ofconnection terminals over a substrate; cutting part of the substrate andpart of the wiring to isolate the plurality of connection terminalselectrically; and connecting an FPC to the plurality of connectionterminals. Furthermore, the semiconductor layer and the wiring arepreferably formed by processing the same metal oxide film.

Effect of the Invention

According to one embodiment of the present invention, the manufacturingyield of a display device can be improved. Alternatively, the resistanceto ESD of a display device can be increased. Alternatively, a displaydevice having high reliability can be provided. Alternatively, a displaydevice having a novel structure can be provided.

Note that the description of the effects does not preclude the existenceof other effects. Note that one embodiment of the present invention doesnot need to have all these effects. Note that effects other than thesecan be derived from the description of the specification, the drawings,the claims, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A to FIG. 1D are diagrams illustrating a structure example of adisplay device.

FIG. 2A to FIG. 2D are diagrams illustrating structure examples of adisplay device.

FIG. 3 is a diagram illustrating a structure example of a displaydevice.

FIG. 4A and FIG. 4B are diagrams illustrating cross-sectional structureexamples of a display device.

FIG. 5A and FIG. 5B are diagrams illustrating cross-sectional structureexamples of a display device.

FIG. 6A and FIG. 6B are diagrams illustrating cross-sectional structureexamples of a display device.

FIG. 7A and FIG. 7B are diagrams illustrating cross-sectional structureexamples of a display device example.

FIG. 8A to FIG. 8C are diagrams illustrating a structure example of adisplay device.

FIG. 9A to FIG. 9C are diagrams illustrating a structure example of adisplay device.

FIG. 10A to FIG. 10L are diagrams illustrating structure examples of awiring.

FIG. 11 is a diagram illustrating a cross-sectional structure example ofa display device.

FIG. 12 is a diagram illustrating a cross-sectional structure example ofa display device.

FIG. 13 is a diagram illustrating a cross-sectional structure example ofa display device.

FIG. 14A to FIG. 14E are diagrams illustrating structure examples of aTEG.

FIG. 15A is a block diagram of a display device. FIG. 15B and FIG. 15Care circuit diagrams of a pixel.

FIG. 16A, FIG. 16C, and FIG. 16D are circuit diagrams of a displaydevice. FIG. 16B is a timing chart.

FIG. 17A and FIG. 17B are diagrams illustrating structure examples of adisplay module.

FIG. 18A to FIG. 18C are diagrams illustrating structure examples of anelectronic device.

FIG. 19A to FIG. 19E are diagrams illustrating structure examples of anelectronic device.

FIG. 20A to FIG. 20G are diagrams illustrating structure examples of anelectronic device.

FIG. 21A to FIG. 21D are diagrams illustrating structure examples of anelectronic device.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments are described with reference to the drawings.Note that the embodiments can be implemented with many different modes,and it is readily understood by those skilled in the art that modes anddetails thereof can be changed in various ways without departing fromthe spirit and scope thereof. Thus, the present invention should not beconstrued as being limited to the following description of theembodiments.

Note that in structures of the invention described below, the sameportions or portions having similar functions are denoted by the samereference numerals in different drawings, and a description thereof isnot repeated. Furthermore, the same hatch pattern is used for theportions having similar functions, and the portions are not especiallydenoted by reference numerals in some cases.

Note that in each drawing described in this specification, the size, thelayer thickness, or the region of each component is exaggerated forclarity in some cases. Therefore, they are not limited to theillustrated scale.

Note that in this specification and the like, the ordinal numbers suchas “first” and “second” are used in order to avoid confusion amongcomponents and do not limit the number.

A transistor is a kind of semiconductor elements and can achieveamplification of current or voltage, switching operation for controllingconduction or non-conduction, or the like. An IGFET (Insulated GateField Effect Transistor) and a thin film transistor (TFT) are in thecategory of a transistor in this specification.

Functions of a “source” and a “drain” are sometimes replaced with eachother when a transistor of opposite polarity is used or when thedirection of current is changed in circuit operation, for example.Therefore, the terms “source” and “drain” can be switched in thisspecification.

Moreover, in this specification and the like, the term “film” and theterm “layer” can be interchanged with each other. For example, in somecases, the term “conductive layer” and the term “insulating layer” canbe interchanged with the term “conductive film” and the term “insulatingfilm,” respectively.

In this specification and the like, a display panel that is oneembodiment of a display device has a function of displaying (outputting)an image or the like on (to) a display surface. Thus, the display panelis one embodiment of an output device.

In this specification and the like, a substrate of a display panel towhich a connector such as an FPC (Flexible Printed Circuit) or a TCP(Tape Carrier Package) is attached, or a substrate on which an IC ismounted by a COG (Chip On Glass) method or the like is referred to as adisplay panel module, a display module, or simply a display panel or thelike in some cases.

Note that in this specification and the like, a touch panel that is oneembodiment of a display device has a function of displaying an image orthe like on a display surface and a function of a touch sensor capableof sensing the contact, press, approach, or the like of a sensing targetsuch as a finger or a stylus with or to the display surface. Therefore,the touch panel is one embodiment of an input/output device.

A touch panel can also be referred to as, for example, a display panel(or a display device) with a touch sensor or a display panel (or adisplay device) having a touch sensor function. A touch panel caninclude a display panel and a touch sensor panel. Alternatively, a touchpanel can have a function of a touch sensor inside a display panel or ona surface thereof

In this specification and the like, a substrate of a touch panel onwhich a connector and an IC are mounted is referred to as a touch panelmodule, a display module, or simply a touch panel or the like in somecases.

Embodiment 1

Described in this embodiment are a structure example of a display deviceof one embodiment of the present invention and an example of amanufacturing method thereof.

One embodiment of the present invention is a display device in which adisplay portion and a plurality of connection terminals are providedover a substrate.

In the display portion, which is a region displaying an image, aplurality of pixels including display elements are arranged in a matrix.The pixel preferably includes one or more display elements and one ormore transistors.

The connection terminal is a terminal to which an FPC (Flexible PrintedCircuit), an IC, or the like is connected. The connection terminal isformed of at least one conductive layer and has an exposed surface.

Furthermore, a first wiring is provided between the connection terminaland the display portion. The first wiring is electrically connected tothe connection terminal and has a function of supplying a signal or apotential having been supplied from the connection terminal to thedisplay portion or a driver circuit for driving the display portion. Thefirst wiring preferably has a low resistance. The first wiring ispreferably positioned on the same plane as that of an electrode and awiring included in the transistor and the display element, for example,and is preferably formed by processing a conductive film that is thesame as the electrode and the wiring.

Furthermore, a second wiring that electrically connects a plurality ofconnection terminals is provided in the manufacturing process of thedisplay device. Owing to the second wiring that electrically connectsthe plurality of connection terminals, an influence of ESD in themanufacturing process of the display device can be reduced, whereby anelement, a wiring, or the like included in the display device can befavorably inhibited from being broken. Examples of processing that cancause ESD in the manufacturing process of the display device include avariety kinds of processing such as substrate transfer, plasma treatmentin deposition, etching, or the like, wet etching treatment, developmenttreatment, and cleaning treatment.

After formation of the display portion, the plurality of connectionterminals, and the like, the second wiring and the substrate arepreferably cut at the same time in the step of division (also referredto as cutting) of the substrate. Accordingly, the plurality ofconnection terminals can be electrically isolated at the same time inthe step of division of the substrate. After that, an FPC or an IC isconnected to the plurality of connection terminals, so that the displaydevice (display module) can be completed.

The second wiring is preferably formed by processing a semiconductorfilm. At this time, the second wiring is preferably formed using asemiconductor film having an increased carrier concentration and alowered resistance.

In particular, the second wiring is preferably formed using asemiconductor film that is the same as a semiconductor layer of atransistor included in the display portion or the driver circuit. Thesemiconductor layer of the transistor includes a channel formationregion in which a channel can be formed, and low-resistance regionsbetween which the channel formation region is provided and which havelower resistances than the channel formation region. The second wiringis preferably formed using a semiconductor film having a loweredresistance like the low-resistance regions of the semiconductor layer.The semiconductor layer may be formed using a silicon (single crystalsilicon, polycrystalline silicon, or amorphous silicon) film, an organicsemiconductor film, or the like; however, it is particularly preferablethat the semiconductor layer be formed using a metal oxide film showingsemiconductor characteristics (also referred to as an oxidesemiconductor film).

After the division of the substrate, a cut surface (also referred to asan end surface or a side surface) of the second wiring is exposed nearan end surface (also referred to as an end portion) of the substrate.Here, in the case where a low-resistance material such as a metal filmis used for the second wiring, electrical noise might be transmittedfrom the exposed end portion of the second wiring to the connectionterminals, or the connection terminals might be electricallyshort-circuited due to a contact of the cut surface of the second wiringwith a housing or components included in a device on which the displaydevice is mounted. By contrast, the problem is less likely to occur inthe display device of one embodiment of the present invention since asemiconductor film having a lower conductivity than a metal film is usedas the second wiring. The contact resistance at the time of being incontact with a metal member can be increased particularly when a metaloxide film is used as the second wiring as compared with the case wherea metal film is used as the second wiring.

At room temperature, the electric resistivity, the resistance value perunit length of the wiring, or the sheet resistance value of the secondwiring is preferably 2 times or more, further preferably 5 times ormore, still further preferably 10 times or more, yet still furtherpreferably 100 times or more, and 10000 times or less, furtherpreferably 5000 times or less, still further preferably 1000 times orless that of the first wiring. For example, a metal oxide film in whichthe electric resistivity calculated from the resistance value or thesheet resistance value is greater than or equal to 1×10⁻⁷ [Ω·m] andlower than or equal to 1×10⁻³ [Ω·m], preferably greater than or equal to1×10⁻⁶ [Ω·m] and lower than or equal to 1×10⁻⁴ [Ω·m] is preferably usedfor the second wiring.

Moreover, part of the FPC that is connected to the connection terminalis preferably provided to overlap with the second wiring remaining onthe substrate side. It is particularly preferable that the part of theFPC extend to a position overlapping with the end surface of thesubstrate and be provided to cover the exposed end surface of the secondwiring. Accordingly, the contact of the housing or the componentsincluded in the device on which the display device is mounted with theend surface of the second wiring can be favorably prevented.

Furthermore, a display device that can be bent (a flexible display) maybe formed by using a flexible material for the substrate. At this time,the substrate includes a support substrate, a support film, a protectivefilm, and the like. Moreover, when a portion of the substrate whichoverlaps with the first wiring (a first portion) is bent to a sideopposite to the display surface side of the display portion so that thefirst wiring is on an outer side, a portion of the substrate whichoverlaps with the connection terminal and the second wiring (a secondportion) can overlap with part of the first wiring or the displayportion. Accordingly, the connection terminal and the FPC can be foldedback to the rear side of the display surface, leading to a reduction insize of the device on which the display device is mounted.

More specific examples of the display device are described below withreference to drawings.

Structure Examples 1 of Display Device

A display device 10 illustrated in FIG. 1A includes a substrate 21, asubstrate 22, a display portion 11, a plurality of connection terminals12, a plurality of wirings 13, and a wiring 14. FIG. 1A corresponds to aperspective view before the cutting of the wiring 14.

The display portion 11 is provided in a region where the substrate 21and the substrate 22 overlap with each other. In the display portion 11,which is a portion displaying an image, a plurality of pixels notillustrated are provided in a matrix. Note that the substrate 22 is notnecessarily provided when not needed.

Examples of the display element provided in the pixel of the displayportion 11 include a liquid crystal element and a light-emittingelement.

Examples of the light-emitting element are self-luminous light-emittingelements such as an LED (Light Emitting Diode), an OLED (Organic LED), aQLED (Quantum-dot LED), and a semiconductor laser.

For the organic EL element (OLED), any of the following structures maybe used: a bottom-emission structure in which light is emitted towardthe formation surface side, a top-emission structure in which light isemitted toward the side opposite to the formation surface side, and adual-emission structure in which light is emitted toward both sides. Inparticular, a light-emitting element having the top-emission structureis preferably used because the aperture ratio can be high, whichfacilitates an increase in definition and enables an increase in theluminance of the light-emitting element.

Examples of the light-emitting diode (LED) include a macro LED (alsoreferred to as a huge LED), a mini LED, a micro LED, and the like indescending order in size. Here, an LED chip whose one side size islarger than 1 mm is called a macro LED, an LED chip whose one side sizeis larger than 100 μm and smaller than or equal to 1 mm is called a miniLED, and an LED chip whose one side size is smaller than or equal to 100μm is called a micro LED. In particular, a mini LED or a micro LED ispreferably used as the LED chip that is applied to the display portion11. The use of a micro LED can achieve an extremely high-definitiondisplay device.

As the display element, a liquid crystal element such as a transmissiveliquid crystal element, a reflective liquid crystal element, or atransflective liquid crystal element can also be used. It is alsopossible to use a MEMS (Micro Electro Mechanical Systems) shutterelement, an optical interference type MEMS element, or a display elementusing a microcapsule method, an electrophoretic method, anelectrowetting method, an Electronic Liquid Powder (registeredtrademark) method, or the like, for instance.

The connection terminals 12, the wirings 13, and the wiring 14 areprovided over the substrate 21. The connection terminals 12 function asterminals electrically connected to an FPC 16 and an IC 19, which aredescribed later, and the like. The connection terminals 12 are providedover a region of the substrate 21 which is not covered with thesubstrate 22.

The wirings 13 electrically connect the connection terminals 12 to thedisplay portion 11 of the display device 10, the driver circuit (notillustrated), or the like.

The wiring 14 has a function of electrically connecting the plurality ofconnection terminals 12. The wiring 14 preferably has a shape thatallows the plurality of connection terminals 12 to be electricallyisolated from each other easily by one cutting step. For example, asillustrated in FIG. 1A, the wiring 14 preferably has a comb-like shapeincluding a plurality of portions extended from the respectiveconnection terminals 12 and a portion in which the plurality of portionsare connected to each other. At this time, the portions of the wiring 14that are extended from the connection terminals 12 are preferablyprovided to intersect with a scribe line (denoted by a dashed-dottedline) of the substrate 21, in which case the wiring 14 can be cutconcurrently in the dividing step of the substrate 21.

FIG. 1B is a perspective view after the cutting of the substrate 21 andthe wiring 14. FIG. 1B shows a substrate 21 a that is separated from thesubstrate 21 and a wiring 14 a after the cutting.

For the cutting of the substrate 21, a scriber, a laser scriber, acutter, a shearing device, or the like can be used. In the case where aflexible film or the like is used for the substrate 21, a cutter, alaser cutter, a lever shear, a punching apparatus, or the like may beused. Examples of the punching apparatus include an apparatus using amold and an apparatus using a Thomson form (a wooden form in which asteel cutter is embedded).

When the wiring 14 is cut at the same time as the division of thesubstrate 21, a plurality of wirings 15 are formed and the plurality ofconnection terminals 12 are electrically isolated from each other on thesubstrate 21 side. One wiring 15 is electrically connected to oneconnection terminal 12. Furthermore, a cut surface (also referred to asa side surface and an end surface) of an end portion of the wiring 15that is on a side opposite to the connection terminal 12 is exposed atan end portion of the substrate 21.

FIG. 1C corresponds to a perspective view after the FPC 16 is attachedto the plurality of connection terminals 12. Note that an IC may beattached separately from the FPC 16, or an FPC on which an IC is mountedmay be attached to the connection terminals 12.

FIG. 1D is a schematic cross-sectional view of a cut surface of thesubstrate 21 of the display device 10 and the vicinity thereof. FIG. 1Dalso clearly shows the substrate 21 a and the wiring 14 a that have beencut.

The display device 10 includes a transistor 30, the wiring 13, theconnection terminal 12, the wiring 15, and the like between thesubstrate 21 and the substrate 22. Furthermore, the substrate 21 and thesubstrate 22 are attached to each other with the bonding layer 25. Thetransistor 30 is a transistor included in a pixel of the display portion11 or a transistor included in a driver circuit for driving the displayportion 11.

The transistor 30 is provided over an insulating layer 41 that is overthe substrate 21 and includes a semiconductor layer 31, a conductivelayer 32, and an insulating layer 33. Part of the conductive layer 32functions as a gate electrode. Part of the insulating layer 33 functionsas a gate insulating layer. A region of the semiconductor layer 31overlapping with the conductive layer 32 functions as a channelformation region. Furthermore, in the semiconductor layer 31, a pair oflow-resistance regions 34 is provided with the channel formation regionprovided therebetween.

For the semiconductor layer 31, a metal oxide exhibiting semiconductorcharacteristics (an oxide semiconductor) is preferably used. Althoughsilicon, an organic semiconductor, or the like may be used for thesemiconductor layer 31, when an oxide semiconductor is used, a highperformance display device can be manufactured at low cost as comparedwith the case where silicon, an organic semiconductor, or the like isused.

The pair of low-resistance regions 34 functions as a source region and adrain region of the transistor 30. The low-resistance regions 34 areregions having lower resistances than the channel formation region. Thelow-resistance regions 34 can also be referred to as regions having ahigher carrier concentration, regions having a larger number of oxygenvacancies, regions having a higher hydrogen concentration, or regionshaving a higher impurity concentration than the channel formationregion.

Furthermore, an insulating layer 42 is provided to cover the transistor30, and the wiring 13 is provided over the insulating layer 42. FIG. 1Dshows an example in which the wiring 13 is electrically connected to thelow-resistance regions 34 of the transistor 30 in an opening provided inthe insulating layer 42. An insulating layer 43 is provided to cover thewiring 13.

FIG. 1D shows an example in which part of the wiring 13 is included inthe connection terminal 12. In the connection terminal 12, part of theinsulating layer 43 that is over the wiring 13 is removed. Note that theexample in which the wiring 13 is electrically connected to one of thesource and the drain of the transistor 30 is shown here; however, thewiring 13 may be electrically connected to a gate of the transistor 30.

Furthermore, the wiring 15 is provided at the end portion of thesubstrate 21. The wiring 15 is provided on the same plane as that of thesemiconductor layer 31 (that is, over the insulating layer 41). Thewiring 15 and the semiconductor layer 31 are preferably formed byprocessing the same semiconductor film. The wiring 15 preferably has alower resistance than the channel formation region like thelow-resistance regions 34 of the semiconductor layer 31. Furthermore,the wiring 15 preferably has a higher resistance than the wiring 13.

Furthermore, the cut surface (also referred to as the end surface andthe side surface) of the wiring 15 is exposed near the end surface (endportion) of the substrate 21. FIG. 1D shows an example in which the sidesurface of the substrate 21, a side surface of the insulating layer 41,the side surface of the wiring 15, a side surface of the insulatinglayer 42, and a side surface of the insulating layer 43 are aligned.Note that sometimes these side surfaces (end surfaces) are not alignedin the case where each insulating layer and the wiring 15 are contractedor extended in the film surface direction depending on stress relaxationat the time of cutting the substrate 21 a. For example, the end surfaceof the wiring 15 is positioned inward or projects outward from the endsurface of the substrate 21 in some cases.

Note that in this specification and the like, the expression “an endportion of a substrate” refers to a region including a range from theend surface of the substrate to a region 10 mm inward from the endsurface, a region including a range from the end surface of thesubstrate to a region 5 mm inward from the end surface, or a regionincluding a range from the end surface of the substrate to a region 3 mminward from the end surface, and a region overlapping with any of theregions of the substrate. Furthermore, the expression “an end surface ofa substrate” also includes the end surface of the substrate.

The FPC 16 is connected to the connection terminal 12 though a connector17. The FPC 16 includes a region overlapping with the wiring 15.Furthermore, the FPC 16 also overlaps with the end surface of thesubstrate 21 and the end surface of the wiring 15 and is provided tocover them. Thus, even when the end surface of the wiring 15 is exposed,the end surface of the wiring 15 is protected by part of the FPC 16, andthus electrical short-circuit of the plurality of wirings 15 due tocontact with a conductive component can be favorably prevented.Moreover, with the structure in which the end surface of the wiring 15is covered with the FPC 16, electrical noise that can be input to thewiring 15 from the outside can be blocked or reduced by the FPC 16 insome cases.

Although the example in which the wiring 14 is cut at the same time asthe cutting of the substrate 21 is described above, the wiring 14 may becut in a step different from the cutting of the substrate 21. In thatcase, the end surface of the wiring 15 is positioned inward from the endsurface of the substrate 21 and the surface is not exposed in somecases.

The top surface shapes of the wiring 15 and the like are describedbelow. FIG. 2A is a schematic top view of the connection terminals 12and the vicinity of the end portion of the substrate 21. Furthermore,FIG. 2A also clearly shows the substrate 21 a that has been divided andthe wiring 14 a that has been cut.

As illustrated in FIG. 2A, the wiring 15 is provided to extend from theconnection terminal 12 to the cut surface (end surface) of the substrate21.

FIG. 2A shows an example in which the width of the wiring 15 is smallerthan that of the connection terminal 12. Furthermore, FIG. 2B shows anexample in which the width of the wiring 15 is made substantially thesame as that of the connection terminal 12. Although not shown here, thewidth of the wiring 15 may be larger than that of the connectionterminal 12. When the width of the wiring 15 is larger, the electricresistance can be smaller. The width of the wiring 15 can be selected inaccordance with the value of the required wiring resistance.

Furthermore, FIG. 2C shows an example in which the arrangement intervalbetween the wirings 15 at the end portion of the substrate 21 isnarrower than the arrangement interval between the connection terminals12. Accordingly, the width of a portion of the wiring 14 to be cut canbe small in the step of dividing the substrate 21; thus, the yield inthe step can be increased.

FIG. 2D shows an example in which the substrate 21 is not cut and onlythe wiring 14 is cut. For example, the wiring 14 is cut with a laserprocessing machine, a cutter, or the like or part of the wiring 14 isremoved by etching, so that only the wiring 14 can be cut without thesubstrate 21 being cut, and the plurality of connection terminals 12 canbe electrically isolated.

Furthermore, in FIG. 2D, a processing trace 14 b that is generated atthe time of cutting the wiring 14 is shown by a dashed line. The shapeof the processing trace 14 b is changed depending on the cutting methodof the wiring 14. For example, in the case where the wiring 14 is cutwith a laser processing machine, a cutter, or the like, an insulatingfilm provided over or below the wiring 14, a flaw, a depression and aprojection, an opening portion, or the like that remains on thesubstrate 21 or the like corresponds to the processing trace 14 b. Inthe case where the wiring 14 is cut by etching, an opening portionprovided in an insulating film or the like that covers the wiring 14corresponds to the processing trace 14 b.

Here, when a plurality of display devices are manufactured using a largesubstrate, the cutting step of the wiring 14 preferably serves also asthe step of dividing the substrate for the respective display devices.Accordingly, the productivity can be increased.

FIG. 3 shows the substrate 21 and the like before the division as anexample. Here, an example in which 3 (in the longitudinal direction)×2(in the lateral direction) display devices (in total, six displaydevices) are formed over one substrate 21 is shown. Furthermore, in FIG.3, a plurality of cut lines 20 a to 20 c are shown by dashed lines.

FIG. 3 shows an example in which the belt-shaped substrate 22 isprovided for a plurality of display devices arranged in the longitudinaldirection. In FIG. 3, the connection terminals 12, part of the wirings13, and the wiring 14 are provided in a region of the substrate 21 thatis not covered with the substrate 22.

The cut line 20 b is a cut line that separates two display devicesadjacent in the lateral direction. The cut line 20 c is a cut line thatseparates two display devices adjacent in the longitudinal direction.The cut line 20 a is a cut line that is parallel to the cut line 20 band divides the substrate 21 and the wiring 14.

Cross-Sectional Structure Examples 1

A more specific cross-sectional structure example of the display device10 is described below.

Structure Example 1

FIG. 4A shows an example of a cross-sectional view of the display device10. FIG. 4A shows an example of a cross-sectional view in a regionincluding the end portion of the substrate 21, the wiring 15, theconnection terminal 12, the wiring 13, and a transistor 30 a provided inthe display portion 11.

Note that a display element in the display portion 11, the substrate 22,and the like are not clearly shown here for simple description.

The transistor 30 a includes the semiconductor layer 31 provided overthe insulating layer 41, the insulating layer 33 over the semiconductorlayer 31, and the conductive layer 32 that is over the insulating layer33 and overlaps with the channel formation region of the semiconductorlayer 31. The semiconductor layer 31 includes the pair of low-resistanceregions 34 between which the channel formation region is positioned.Part of the conductive layer 32 functions as a gate electrode and partof the insulating layer 33 functions as a gate insulating layer.

The transistor 30 a is what is called a top-gate transistor, in whichthe gate electrode is included over the semiconductor layer 31.

Furthermore, the insulating layer 33 is processed so that the topsurface shape of the insulating layer 33 is substantially the same asthat of the conductive layer 32. The insulating layer 42 is provided tocover the transistor 30 a and is provided in contact with the topsurfaces of the low-resistance regions 34 of the semiconductor layer 31.A pair of conductive layers 35 functioning as a source electrode and adrain electrode is provided over the insulating layer 41. The conductivelayers 35 are electrically connected to the low-resistance regions 34through openings provided in the insulating layer 42.

Note that in this specification and the like, the expression “havingsubstantially the same top surface shapes” means that at least outlinesof stacked layers partly overlap with each other. For example, the caseof processing an upper layer and a lower layer with the use of the samemask pattern or mask patterns that are partly the same is included.However, in some cases, the outlines do not completely overlap with eachother and the upper layer is positioned on an inner side of the lowerlayer or the upper layer is positioned on an outer side of the lowerlayer; such a case is also represented by the expression “the top-viewshapes are substantially the same.”

The wiring 13 that is electrically connected to the connection terminal12 is positioned on the same plane as that of the pair of conductivelayers 35 that is electrically connected to the transistor 30 a (thatis, over the insulating layer 42). Here, the wiring 13 and theconductive layers 35 are preferably formed by processing the sameconductive film.

Furthermore, the insulating layer 43 is provided to cover the insulatinglayer 42 and the conductive layer 35. The insulating layer 43 mayfunction as a planarization layer. A conductive layer 38 is providedover the insulating layer 43. The conductive layer 38 can be used as apixel electrode, a wiring, or the like.

The connection terminal 12 has a stacked-layer structure in which aconductive layer 32 p, a conductive layer 35 p, and a conductive layer38 p are stacked.

The conductive layer 32 p is positioned on the same plane as that of theconductive layer 32. In that case, the conductive layer 32 p and theconductive layer 32 are preferably formed by processing the sameconductive film.

The conductive layer 35 p constitutes part of the wiring 13. Theconductive layer 35 p is electrically connected to the conductive layer32 p through an opening provided in the insulating layer 42. Theconductive layer 35 p is positioned on the same plane as that of theconductive layer 35. In that case, the conductive layer 35 p and theconductive layer 35 are preferably formed by processing the sameconductive film.

The conductive layer 38 p is provided over the insulating layer 43 andis electrically connected to the conductive layer 35 p through anopening provided in the insulating layer 43. The conductive layer 38 pis positioned on the same plane as that of the conductive layer 38. Inthat case, the conductive layer 38 p and the conductive layer 38 arepreferably formed by processing the same conductive film.

Here, a conductive material that is not easily oxidized or a conductivematerial that maintains the conductivity even when oxidized ispreferably used for the surface of the connection terminal 12. Inparticular, a conductive oxide or a conductive nitride is preferablyused for the conductive layer positioned on the surface side of theconnection terminal 12.

In the structure of the connection terminal 12 illustrated in FIG. 4A,the exposed surface of the conductive layer 38 p corresponds to aportion connected to the FPC 16 and the like. Thus, a conductive oxidematerial or the like is preferably used for at least the top of theconductive layer 38 p. For example, it is preferable that astacked-layer structure including a conductive film containing a metalor an alloy and a conductive film containing a conductive oxide be usedfor the conductive layer 38 p because the electric resistance can bereduced.

Note that the structure of the connection terminal 12 is not limited tothis as long as the connection terminal 12 includes at least one of theconductive layer 32 p, the conductive layer 35 p, and the conductivelayer 38 p. In particular, the conductive layer 35 p is preferablyincluded.

The wiring 15 is provided at the end portion of the substrate 21. FIG.4A shows an example in which the substrate 21, the insulating layer 41,the wiring 15, the insulating layer 42, and the insulating layer 43 arestacked at the end portion of the substrate 21 and these end surfaces(cut surfaces) are substantially aligned.

The wiring 15 is positioned on the same plane as that of thesemiconductor layer 31 of the transistor 30 a (here, over the insulatinglayer 41). In particular, the wiring 15 and the semiconductor layer 31are preferably formed by processing the same film. Furthermore, thewiring 15 preferably has a low resistance, like the low-resistanceregions 34 included in the semiconductor layer 31.

In FIG. 4A, a connection portion 18 for the conductive layer 35 p andthe wiring 15 is shown by a dashed line. Here, in the connection portion18, the conductive layer 35 p and the wiring 15 are electricallyconnected to each other through an opening provided in the insulatinglayer 42.

Structure Example 2

FIG. 4B differs from FIG. 4A mainly in part of the structure of thetransistor and part of the structure of the connection terminal 12.

A transistor 30 b illustrated in FIG. 4B includes a conductive layer 36that is between the substrate 21 and the insulating layer 41 andoverlaps with the channel formation region of the semiconductor layer31. In the transistor 30 b, the conductive layer 36 functions as a firstgate electrode, and the conductive layer 32 functions as a second gateelectrode. At this time, part of the insulating layer 41 functions as afirst gate insulating layer, and part of the insulating layer 33functions as a second gate insulating layer.

Different potentials or signals may be supplied to the conductive layer32 and the conductive layer 36. Alternatively, the conductive layer 32and the conductive layer 36 may be electrically connected to each otherto be supplied with the same potential or signal. Alternatively, theconductive layer 36 may be electrically connected to one of the pair ofconductive layers 35.

The connection terminal 12 includes a conductive layer 36 p. Theconductive layer 36 p is positioned on the same plane as that of theconductive layer 36. In that case, the conductive layer 36 p and theconductive layer 36 are preferably formed by processing the sameconductive film.

The conductive layer 36 p and the conductive layer 32 p are electricallyconnected to each other through an opening provided in part of theinsulating layer 41 and part of the insulating layer 33.

Structure Example 3

FIG. 5A differs from FIG. 4A mainly in part of the transistor structure.

In a transistor 30 c illustrated in FIG. 5A, the insulating layer 33 isprovided to cover a top surface and a side surface of the semiconductorlayer 31 (that is, top surfaces and side surfaces of the low-resistanceregions 34). Furthermore, a top surface and a side surface of the wiring15 are also covered with the insulating layer 33.

Structure Example 4

FIG. 5B differs from FIG. 4B mainly in part of the transistor structure.

In a transistor 30 d illustrated in FIG. 5B, the insulating layer 33 isprovided to cover a top surface and a side surface of the semiconductorlayer 31 (that is, top surfaces and side surfaces of the low-resistanceregions 34). Furthermore, a top surface and a side surface of the wiring15 are also covered with the insulating layer 33.

Structure Example 5

FIG. 6A is an example in which a transistor 40 having a structuredifferent from the above is used.

The transistor 40 includes the conductive layer 32 provided over thesubstrate 21, the insulating layer 33 that covers the conductive layer32, the semiconductor layer 31 that is positioned over the insulatinglayer 33 and includes a region overlapping with the conductive layer 32,and the pair of conductive layers 35 that is in contact with a topsurface of the semiconductor layer 31.

The transistor 40 is what is called a bottom-gate transistor including agate electrode below the semiconductor layer 31.

A region of the semiconductor layer 31 that overlaps with the conductivelayer 32 and is not in contact with the conductive layers 35 functionsas a channel formation region. Furthermore, regions of the semiconductorlayer 31 that are in contact with the conductive layers 35 functions asthe low-resistance regions 34.

Furthermore, an insulating layer 45 is provided to cover the transistor40, and the insulating layer 43 and the conductive layer 38 are providedover the insulating layer 45. Part of the insulating layer 45 isprovided in contact with the top surface of the channel formation regionof the semiconductor layer 31.

The connection terminal 12 includes the conductive layer 32 p, theconductive layer 35 p, and the conductive layer 38 p. The conductivelayer 32 p and the conductive layer 35 p are electrically connected toeach other through an opening provided in the insulating layer 33. Theconductive layer 35 p and the conductive layer 38 p are electricallyconnected to each other through an opening provided in the insulatinglayer 45 and the insulating layer 43.

The wiring 15 is provided over the insulating layer 33. Furthermore, inthe connection portion 18, the conductive layer 35 p and the wiring 15are in contact with each other and are electrically connected to eachother.

Here, in the case of a structure in which the insulating layer 45 is incontact with a top surface of the wiring 15, a stacked-layer structurethat is similar to that of the channel formation region of thetransistor 40 is formed, leading to an increase in the resistance of thewiring 15 in some cases. Thus, the insulating layer 45 is preferablyprocessed not to be in contact with the top surface of the wiring 15 asillustrated in FIG. 6A. FIG. 6A shows an example in which the insulatinglayer 43 is provided in contact with the top surface of the wiring 15.

Structure Example 6

FIG. 6B differs from FIG. 6A mainly in that an insulating layer 46 isincluded instead of the insulating layer 43 and that a conductive layer37 is included.

The insulating layer 46 functions as a barrier film preventing diffusionof water, hydrogen, or the like from the outside. Furthermore, theinsulating layer 46 may have a function of releasing oxygen contained inthe insulating layer 45 to the outside.

A transistor 40 a includes the conductive layer 37 functioning as asecond gate electrode. The conductive layer 37 includes a regionoverlapping with the channel formation region of the semiconductor layer31 with the insulating layer 45 and the insulating layer 46 positionedtherebetween. The conductive layer 37 and the conductive layer 38 arepreferably formed by processing the same conductive film.

The connection terminal 12 includes the conductive layer 32 p, theconductive layer 35 p, and the conductive layer 38 p. The conductivelayer 35 p and the conductive layer 38 p are electrically connected toeach other through an opening provided in the insulating layer 45 andthe insulating layer 46.

The insulating layer 45 is processed not to be in contact with the topsurface of the wiring 15. Furthermore, the insulating layer 46 isprovided to extend beyond the end portion of the insulating layer 45 andbe in contact with the top surface of the wiring 15.

MODIFICATION EXAMPLES

Examples in which the semiconductor layer 31 of the transistor and thewiring 15 are formed by processing different films are described below.

Modification Example 1

FIG. 7A differs from the structure illustrated in FIG. 6A mainly in thata conductive layer 39 and the insulating layer 46 are included.

A transistor 40 b illustrated in FIG. 7A includes the conductive layer39 functioning as a second gate electrode. The conductive layer 39 isprovided over the insulating layer 45 and includes a portion overlappingwith the channel formation region of the semiconductor layer 31 with theinsulating layer 45 positioned therebetween. Furthermore, the insulatinglayer 46 is provided in contact with a top surface and a side surface ofthe conductive layer 39.

The conductive layer 39 preferably contains a material similar to thatof the semiconductor layer 31. In particular, the conductive layer 39and the semiconductor layer 31 preferably contain metal oxides one ormore metal elements of which are the same as each other. It isparticularly preferable that the conductive layer 39 and thesemiconductor layer 31 have substantially the same metal elementcomposition (content percentage).

The connection terminal 12 includes the conductive layer 32 p, theconductive layer 35 p, and the conductive layer 38 p. The conductivelayer 35 p is electrically connected to the conductive layer 38 pthrough an opening provided in the insulating layer 45, the insulatinglayer 46, and the insulating layer 43.

The wiring 15 a is provided at the end portion of the substrate 21. Thewiring 15 a is provided over the insulating layer 45. The wiring 15 aand the conductive layer 39 are preferably formed by processing the sameconductive film. The insulating layer 46 is provided in contact with atop surface and a side surface of the wiring 15 a.

Furthermore, in the connection portion 18, the conductive layer 35 p andthe wiring 15 a are electrically connected to each other through anopening provided in the insulating layer 45.

Modification Example 2

FIG. 7B shows an example in which the wiring 15 a extends to theconnection terminal 12.

The connection terminal 12 includes the conductive layer 32 p, theconductive layer 35 p, part of the wiring 15 a, and the conductive layer38 p. The conductive layer 35 p and the part of the wiring 15 a areelectrically connected to each other through an opening provided in theinsulating layer 45. The wiring 15 a and the conductive layer 38 p areelectrically connected to each other through an opening provided in theinsulating layer 46 and the insulating layer 43.

With such a structure, the connection terminal 12 can also serve as theconnection portion 18.

In each structure example and each modification example exemplifiedhere, the connection terminal and the wiring electrically connected tothe connection terminal can be formed using the conductive film, thesemiconductor film, or the like included in the transistor or the pixelincluded in the display portion. Thus, the connection terminal and thewiring can be formed without an increase in steps; thus, themanufacturing cost is not increased, and the display device having highreliability can be manufactured at low cost.

Structure Examples 2 of Display Device

Structure examples of a display device that has flexibility and can bebent are described below.

Structure Example 1

FIG. 8A is a schematic top view of a display device 10 a. The displaydevice 10 a includes a substrate 51 having flexibility. The displayportion 11, a pair of circuit portions 52, a circuit portion 53, theplurality of wirings 13, the plurality of connection terminals 12, andthe plurality of wirings 15 are provided over the substrate 51.

The circuit portions 52 and the circuit portion 53 have a function ofdriving the display portion 11. Two circuit portions 52 are providedwith the display portion 11 positioned therebetween. The circuit portion53 is provided between the display portion 11 and the wirings 13. Thecircuit portions 52 function as gate drivers, for example, and thecircuit portion 53 functions as a source driver or part of the sourcedriver, for example. For example, the circuit portion 53 may include abuffer circuit or a demultiplexer circuit.

As a display element provided in the display portion 11, theabove-described variety of display elements such as a liquid crystalelement and a light-emitting element can be used. In particular, anorganic EL element is preferably used as the display element.

In the top surface shape, a portion of the substrate 51 over which thewirings 13, the connection terminals 12, and the wirings 15 are providedprojects from the other portion. In other words, the width of theportion of the substrate 51 is smaller than the width of a portion ofthe substrate 51 over which the display portion 11 is provided.

Furthermore, the projecting portion of the substrate 51 includes aregion that can be bent (a bent portion 50 a) in a region overlappingwith the wirings 13. Moreover, the substrate 51 includes a pair ofregions that can be bent (bent portions 50 b) in a region over which thedisplay portion 11 is provided. As illustrated in FIG. 8A, owing to theprojecting shape of the part of the substrate 51, the bending directionof the bent portion 50 a can intersect with the bending direction of thebent portions 50 b.

FIG. 8B and FIG. 8C are perspective views of the display device 10 a inthe case where the substrate 51 is bent at the bent portion 50 a and thebent portions 50 b to a side opposite to the display surface side. FIG.8B is a perspective view including the display surface side, and FIG. 8Cis a perspective view including the side opposite to the display surfaceside. Furthermore, FIG. 8C clearly shows the FPC 16 connected to theconnection terminals 12.

When both sides of the display portion 11 are bent as illustrated inFIG. 8B, at the time of incorporating the display device 10 a in anelectronic device, bent display portions can be provided on both sidesof the electronic device. Thus, a highly functional electronic devicecan be provided.

Furthermore, as illustrated in FIG. 8B and FIG. 8C, owing to the bentportion 50 a, part of the substrate 51 can be folded back to the sideopposite to the display surface side. Specifically, the projectingportion of the substrate 51 can be folded back so that the wirings 13are on an outer side. Accordingly, the connection terminals 12 and thewirings 15 can be placed on the side opposite to the display surfaceside; in addition, the FPC 16 can be placed on the side opposite to thedisplay surface side. Thus, the area of a non-display portion can bereduced when the display device 10 a is incorporated in an electronicdevice.

Furthermore, as illustrated in FIG. 8C, on the side opposite to thedisplay surface side, part of the FPC 16 can cover an end portion of thesubstrate 51. Accordingly, even in the case where part of the wirings 15(the end surface, the cut surface, or the like) are exposed, contactwith a component such as a housing of an electronic device can beprevented; thus, the electronic device can have high reliability.

FIG. 8C shows an example in which the IC 19 is mounted on the FPC 16.The IC 19 is formed over a single crystal semiconductor substrate, forexample, and includes a semiconductor chip including a circuitfunctioning as a source driver.

Structure Example 2

FIG. 9A, FIG. 9B and FIG. 9C show a top view and perspective views of adisplay device 10 b having a structure partly different from the above.

The display device 10 b includes connection terminals 12 a to which theFPC 16 is connected and connection terminals 12 b to which the IC 19 isconnected in a projecting portion of the substrate 51. Furthermore, eachof the plurality of wirings 15 is electrically connected to theconnection terminal 12 a or the connection terminal 12 b. Accordingly,the IC 19 can be mounted on the substrate 51 as illustrated in FIG. 9C.

Furthermore, a notch 54 is provided in the substrate 51. The notch 54 isa portion in which, for example, a lens of a camera included in anelectronic device, a variety of sensors such as an optical sensor, alighting device, a design, or the like can be placed. Owing to the notchof part of the display portion 11, a further highly designed electronicdevice can be provided. In addition, owing to the notch, the screenoccupation ratio with respect to the surface of a housing of anelectronic device can be increased.

Structure Examples of Wiring

In the display device 10 a and the display device 10 b that aredescribed above, when the bent portion 50 a is bent with a smallercurvature radius, the thickness of the display device 10 a or thedisplay device 10 b including the projecting portion can be smaller;thus, flexibility in designing an electronic device can be increased. Incontrast, due to the small curvature radius of the bent portion 50 a,the wirings 13 placed in the bent portion 50 a might be disconnected.Structure examples of the wirings 13 that can be favorably used for thebent portion 50 a are described below.

FIG. 10A to FIG. 10L show the top surface shapes of two adjacent wirings13 including a portion placed in the bent portion 50 a.

Each of the wirings 13 illustrated in FIG. 10A has a narrower shape(small width) in the bent portion 50 a than in other portions.Accordingly, cracks are less likely to occur when the wiring 13 is bent;thus, the strength can be increased.

In the wirings 13 illustrated in FIG. 10B, FIG. 10C, and FIG. 10D,openings 13 a provided in the range of the bent portion 50 a in theextending direction of the wirings 13 are provided. In other words, eachof the wirings 13 has a shape of a plurality of branched narrowportions. With such a structure, even when part of any of the wirings 13is disconnected, conduction can be maintained by the other part.

Furthermore, each of the openings 13 a is a portion having high adhesionbecause the insulating layer positioned below the wirings 13 (forexample, the insulating layer 42) and the insulating layer positionedover the wirings 13 (for example, the insulating layer 43) are incontact with each other. Thus, each of the branched narrow portions ofthe wiring 13 placed in the bent portion 50 a can be positioned betweenthe portions having high adhesion; accordingly, film separation of thewirings 13 can be inhibited in the bent portion 50 a.

FIG. 10B shows an example in which one opening 13 a is provided toextend over the bent portion 50 a so that the wiring 13 is branched intotwo. FIG. 10C shows an example in which two openings 13 a are providedto extend over the bent portion 50 a so that the wiring 13 is branchedinto three. FIG. 10C shows an example in which three openings 13 a areprovided to extend over the bent portion 50 a so that the wiring 13 isbranched into four. Note that the structure is not limited thereto, andfour or more openings 13 a may be provided.

Moreover, in FIG. 10D, portions of the wirings 13 that are placed in thebent portion 50 a have shapes of expanding in the width direction.Accordingly, the widths of the plurality of branched portions can beincreased, so that the wiring resistance can be low.

FIG. 10E and FIG. 10F each show an example in which a plurality ofopenings 13 b are provided in the wiring 13. The length of each of theopenings 13 b in the extending direction of the wirings 13 is shorterthan the length of the bent portion 50 a. Accordingly, the strength ofthe wirings 13 and the adhesion can be increased and the wiringresistance can be reduced.

FIG. 10E shows an example in which the openings 13 b on the left and theopenings 13 b on the right are placed in a staggered manner.Furthermore, FIG. 10F shows an example in which the openings 13 b areplaced in alignment, so that the wiring 13 has a checkered shape.

FIG. 10G and FIG. 10H each show an example in which both of the openings13 a extending over the bent portion 50 a and the openings 13 b eachhaving a length shorter than the bent portion 50 a are provided. Withsuch a structure, the adhesion can be further increased.

FIG. 10G shows an example in which the openings 13 b having the sameshape are placed to extend over the bent portion 50 a. Note that thestructure is not limited thereto, and the openings 13 b having differentshapes may be arranged in the extending direction of the wirings 13. Asan example, FIG. 10H shows an example in which the opening 13 b that iscloser to the center portion of the bent portion 50 a has a smallerlength.

FIG. 10I and FIG. 10J each show an example in which a narrow portion anda wide portion are alternately repeated in the wirings 13. With such astructure, the narrow portions of the wirings 13 can be portions havinghigh adhesion; thus, the film separation of the wirings 13 can beinhibited. Furthermore, providing such a plurality of narrow portionscan increase not only the strength against the bending in the extendingdirection of the wirings 13 but also the strength against twisting.

FIG. 10I shows a case where two adjacent wirings 13 have the same shape.FIG. 10J shows a case of a different shape in which the wide portionsand the narrow portions of two wirings 13 are placed in a staggeredmanner. With the structure illustrated in FIG. 10J, the interval betweentwo adjacent wirings can be narrowed, leading to an increase in wiringdensity.

FIG. 10K and FIG. 10L each show an example in which the wirings 13include a plurality of intersecting portions 13 c. Furthermore,substantially rhombic openings 13 d are provided with one intersectingportion positioned therebetween. With such a structure, the wiring 13can have high strength against bending and twisting, high adhesion, andlow wiring resistance.

FIG. 10K shows an example of a shape in which the intersecting portions13 c are arranged in a line in the extending direction of the wirings13. FIG. 10L shows an example of a shape in which the intersectingportions 13 c are arranged in a plurality of rows (here, three rows) inthe extending direction of the wirings 13.

Here, as illustrated in each diagram of FIG. 10, the outlines of thewirings 13 and the outlines of the opening portions preferably each havea rounded shape such as a curved shape or an arc without including anangular portion (a portion having an acute angle or a portion having anobtuse angle). When the wirings 13 have angular portions, the angularportion becomes a starting point of a crack at the time of applicationof external force, and at worst, the wirings 13 might be disconnected.Thus, when the outlines of the wirings 13 and the outlines of theopening portions each have a rounded shape, a crack is less likely tooccur in the wirings 13.

The above is the description of the structure examples of the wiring.

Cross-Sectional Structure Examples 2

More specific examples of a cross-sectional structure of the displaydevice are described below.

Structure Example 1

FIG. 11 is a schematic cross-sectional view of the display device 10 a.FIG. 11 corresponds to a cross section taken along dashed-dotted lineS-T of the display device 10 a illustrated in FIG. 8A.

FIG. 11 shows a cross section including the display portion 11, thecircuit portion 52, the bent portion 50 a, and the connection terminal12. A transistor 750 and a capacitor 790 are provided in the displayportion 11. A transistor 752 is provided in the circuit portion 52. AnFPC 716 is connected to the connection terminal 12 through a connector780.

The transistor 750 and the transistor 752 are each a transistor using anoxide semiconductor for a semiconductor layer in which a channel isformed. Note that the transistors are not limited thereto, and atransistor using silicon (amorphous silicon, polycrystalline silicon, orsingle-crystal silicon) or a transistor using an organic semiconductorfor the semiconductor layer can be used.

The transistor used in this embodiment includes a highly purified oxidesemiconductor film in which formation of oxygen vacancies is inhibited.The off-state current of the transistors can be reduced significantly.Accordingly, in the pixel employing such a transistor, the retentiontime of an electrical signal such as an image signal can be extended,and the interval between writes of an image signal or the like can alsobe set longer. Accordingly, the frequency of refresh operations can bereduced, so that power consumption can be reduced.

The transistor used in this embodiment can have relatively highfield-effect mobility and thus is capable of high-speed operation. Forexample, with the use of such a transistor capable of high-speedoperation for a display device, a switching transistor in a pixel and adriver transistor used in a circuit portion can be formed over onesubstrate. That is, a structure in which a driver circuit formed using asilicon wafer or the like is not used is possible, in which case thenumber of components of the display device can be reduced. Moreover, theuse of the transistor capable of high-speed operation also in the pixelcan provide a high-quality image.

The capacitor 790 includes a lower electrode formed by processing thesame film as a film used for the first gate electrode of the transistor750 and an upper electrode formed by processing the same metal oxidefilm as a film used for the semiconductor layer. The upper electrode hasreduced resistance like a source region and a drain region of thetransistor 750. Part of an insulating film functioning as a first gateinsulating layer of the transistor 750 is provided between the lowerelectrode and the upper electrode. That is, the capacitor 790 has astacked-layer structure in which an insulating film functioning as adielectric film is positioned between a pair of electrodes. A wiringobtained by processing the same film as a film used for a sourceelectrode and a drain electrode of the transistor 750 is connected tothe upper electrode.

An insulating layer 770 that functions as a planarization film isprovided over the transistor 750, the transistor 752, and the capacitor790.

The transistor 750 in the display portion 11 and the transistor 752 inthe circuit portion 52 may have different structures. For example, atop-gate transistor may be used as one of the transistors 750 and 752,and a bottom-gate transistor may be used as the other. Note that thisdescription as for the circuit portions 52 can be applied to the circuitportion 53.

Note that Cross-sectional structure example 1, which is described above,can be referred to for the structures of the transistor 750 and thetransistor 752.

Cross-sectional structure example 1 and the modification examples, whichare described above, can be referred to for the structures of the wiring13, the connection terminal 12, and the wiring 15.

The display device 10 a includes the substrate 51 and a substrate 740,each of which functions as a support substrate. As the substrate 51 andthe substrate 740, a glass substrate or a substrate having flexibilitysuch as a plastic substrate can be used, for example.

The transistor 750, the transistor 752, the capacitor 790, and the likeare provided over the insulating layer 744. The substrate 51 and theinsulating layer 744 are bonded to each other with the adhesive layer742.

The display device 10 a includes a light-emitting element 782, acoloring layer 736, a light-blocking layer 738, and the like.

The light-emitting element 782 includes a conductive layer 772, an ELlayer 786, and a conductive layer 788. The conductive layer 772 iselectrically connected to the source electrode or the drain electrodeincluded in the transistor 750. The conductive layer 772 is providedover the insulating layer 770 and functions as a pixel electrode. Aninsulating layer 730 is provided to cover an end portion of theconductive layer 772. Over the insulating layer 730 and the conductivelayer 772, the EL layer 786 and the conductive layer 788 are stacked.

For the conductive layer 772, a material having a property of reflectingvisible light can be used. For example, a material containing aluminum,silver, or the like can be used. For the conductive layer 788, amaterial that transmits visible light can be used. For example, an oxidematerial containing indium, zinc, tin, or the like is preferably used.Thus, the light-emitting element 782 is a top-emission light-emittingelement, which emits light to the side opposite the formation surface(the substrate 740 side).

The EL layer 786 contains an organic compound or an inorganic compoundsuch as quantum dots. The EL layer 786 contains a light-emittingmaterial that exhibits light when current flows.

As the light-emitting material, a fluorescent material, a phosphorescentmaterial, a thermally activated delayed fluorescence (TADF) material, aninorganic compound (e.g., a quantum dot material), or the like can beused. Examples of materials that can be used for quantum dots include acolloidal quantum dot material, an alloyed quantum dot material, acore-shell quantum dot material, and a core quantum dot material.

The light-blocking layer 738 and the coloring layer 736 are provided onone surface of an insulating layer 746. The coloring layer 736 isprovided in a position overlapping with the light-emitting element 782.The light-blocking layer 738 is provided in a region not overlappingwith the light-emitting element 782 in the display portion 11. Thelight-blocking layer 738 may also be provided to overlap with thecircuit portion 52 or the like.

The substrate 740 is bonded to the other surface of the insulating layer746 with an adhesive layer 747. The substrate 740 and the substrate 51are bonded to each other with a sealing layer 732.

Here, for the EL layer 786 included in the light-emitting element 782, alight-emitting material that exhibits white light emission is used.White light emission by the light-emitting element 782 is colored by thecoloring layer 736 to be emitted to the outside. The EL layer 786 isprovided over the pixels that exhibit different colors. The pixelsprovided with the coloring layer 736 transmitting any of red light (R),green light (G), and blue light (B) are arranged in a matrix in thedisplay portion 11, whereby the display device 10 a can performfull-color display.

A conductive film having a transmissive property and a reflectiveproperty may be used for the conductive layer 788. In this case, amicrocavity structure is achieved between the conductive layer 772 andthe conductive layer 788 such that light of a specific wavelength can beintensified to be emitted. Also in this case, an optical adjustmentlayer for adjusting an optical distance may be placed between theconductive layer 772 and the conductive layer 788 such that thethickness of the optical adjustment layer differs between pixels ofdifferent colors and accordingly the color purity of light emitted fromeach pixel can be increased.

Note that a structure in which the coloring layer 736 or the aboveoptical adjustment layer is not provided may be employed when the ELlayer 786 is formed into an island shape for each pixel or into a stripeshape for each pixel column, i.e., the EL layer 786 is formed byseparate coloring.

Here, an inorganic insulating film that functions as a barrier filmhaving low permeability is preferably used for each of the insulatinglayer 744 and the insulating layer 746. With such a structure in whichthe light-emitting element 782, the transistor 750, and the like areinterposed between the insulating layer 744 and the insulating layer746, deterioration of them can be inhibited and a highly reliabledisplay device can be achieved.

Structure Example 2

FIG. 12 is a cross-sectional view of the display device 10 a having astructure partly different from that of FIG. 11. Furthermore, FIG. 12clearly shows an embodiment in which part of the display device 10 a isbent in the bent portion 50 a and folded back to the side opposite tothe display surface side.

In the display device 10 a illustrated in FIG. 12, a resin layer 743 isprovided between the adhesive layer 742 and the insulating layer 744illustrated in FIG. 11. A protection layer 749 is provided instead ofthe substrate 740.

The resin layer 743 is a layer containing an organic resin such aspolyimide or acrylic. The insulating layer 744 contains an inorganicinsulating material such as silicon oxide, silicon oxynitride, siliconnitride, or the like. The resin layer 743 and the substrate 51 areattached to each other with the bonding layer 742. The resin layer 743is preferably thinner than the substrate 51.

The protection layer 749 is attached to the sealing layer 732. A glasssubstrate, a resin film, or the like can be used as the protection layer749. As the protection layer 749, an optical member such as a polarizingplate (including a circularly polarizing plate) or a scattering plate,an input device such as a touch sensor panel, or a structure in whichtwo or more of the above are stacked may be employed. Furthermore, theprotection layer 749 may include a component included in part of ahousing of an electronic device (for example, a portion to be a screen).

The EL layer 786 included in the light-emitting element 782 is providedover the insulating layer 730 and the conductive layer 772 in an islandshape. The EL layers 786 are formed separately so that respectivesubpixels emit light of different colors, whereby color display can beperformed without use of the coloring layer 736.

A protective layer 741 is provided to cover the light-emitting element782. The protective layer 741 has a function of preventing diffusion ofimpurities such as water into the light-emitting element 782. Theprotection layer 741 has a stacked-layer structure in which aninsulating layer 741 a, an insulating layer 741 b, and an insulatinglayer 741 c are stacked in this order from the conductive layer 788side. In that case, it is preferable that inorganic insulating filmswith a high barrier property against impurities such as water be used asthe insulating layer 741 a and the insulating layer 741 c, and anorganic insulating film that functions as a planarization film be usedas the insulating layer 741 b. The protection layer 741 is preferablyprovided to extend also to the circuit portion 52 and the like.

An organic insulating film covering the transistor 750, the transistor752, and the like is preferably formed in an island shape inward fromthe sealing layer 732. In other words, an end portion of the organicinsulating film is preferably inward from the sealing layer 732 or in aregion overlapping with an end portion of the sealing layer 732. FIG. 12shows an example in which the insulating layer 770, the insulating layer730, and the insulating layer 741 b are processed into island shapes.The insulating layer 741 c and the insulating layer 741 a are providedin contact with each other in a portion overlapping with the sealinglayer 732, for example. Thus, a surface of the organic insulating filmcovering the transistor 750 and the transistor 752 is not exposed to theoutside of the sealing layer 732, whereby diffusion of water or hydrogenfrom the outside to the transistor 750 and the transistor 752 throughthe organic insulating film can be favorably prevented. This can reducevariations in electrical characteristics of the transistors, so that adisplay device with extremely high reliability can be fabricated.

In FIG. 12, the bent portion 50 a includes a portion where the substrate51, the bonding layer 742, and the inorganic insulating film such as theinsulating layer 744 are not provided. The bent portion 50 a has astructure in which the insulating layer 770 including an organicmaterial covers the wiring 13 so that the wiring 13 is not exposed. Inthe structure illustrated in FIG. 12, the bent portion 50 a has astacked-layer structure in which the resin layer 743, the wiring 13, andthe insulating layer 770 are stacked.

When a structure is employed in which an inorganic insulating film isnot provided if possible in the bent portion 50 a and only a conductivelayer containing a metal or an alloy and a layer containing an organicmaterial are stacked, generation of cracks caused at bending can beprevented. When the substrate 51 is not provided in the bent portion 50a, part of the display device 10 a can be bent with an extremely smallradius of curvature.

In a region overlapping with the connection terminal 12, a support 720is bonded to the resin layer 743 with a bonding layer 748 positionedtherebetween. A material having higher rigidity than the substrate 51and the like can be used for the support 720. Alternatively, the support720 may be part of a housing of an electronic device or part of acomponent placed in an electronic device.

In FIG. 12, a conductive layer 761 is provided over the protection layer741. The conductive layer 761 can be used as a wiring or an electrode.

In the case where a touch sensor is provided so as to overlap with thedisplay device 10 a, the conductive layer 761 can function as anelectrostatic shielding film for preventing transmission of electricalnoise to the touch sensor during pixel driving. In this case, thestructure in which a predetermined constant potential is applied to theconductive layer 761 can be employed.

Alternatively, the conductive layer 761 can be used as an electrode ofthe touch sensor, for example. This enables the display device 10 a tofunction as a touch panel. For example, the conductive layer 761 can beused as an electrode or a wiring of a capacitive touch sensor. In thiscase, the conductive layer 761 can be used as a wiring or an electrodeto which a sensor circuit is connected or a wiring or an electrode towhich a sensor signal is input. When the touch sensor is formed over thelight-emitting element 782 in this manner, the number of components canbe reduced, and manufacturing cost of an electronic device or the likecan be reduced.

The conductive layer 761 is preferably provided in a portion notoverlapping with the light-emitting element 782. The conductive layer761 can be provided in a position overlapping with the insulating layer730, for example. Thus, a transparent conductive film with a relativelylow conductivity is not necessarily used for the conductive layer 761,and a metal or an alloy having high conductivity or the like can beused, so that the sensitivity of the sensor can be increased.

As the type of the touch sensor that can be formed of the conductivelayer 761, a variety of types such as a resistive type, a surfaceacoustic wave type, an infrared type, an optical type, and apressure-sensitive type can be used, without limitation to a capacitivetype. Alternatively, two or more of these types may be combined andused.

Structure Example 3

FIG. 13 illustrates a schematic cross-sectional view of the displaydevice 10 b in the case where a liquid crystal element is used as adisplay element. FIG. 13 illustrates a cross-sectional view of a regionincluding the circuit portion 52, the display portion 11, and theconnection terminal 12.

The display device 10 b illustrated in FIG. 13 includes a transistor721, a transistor 722, a liquid crystal element 710, and the likebetween a substrate 701 and a substrate 705. The substrate 701 and thesubstrate 705 are bonded to each other with the sealing layer 732.

Here, an example in which bottom-gate transistors are used as thetransistor 721 and the transistor 722. Cross-sectional structure example1, which is described above, can be referred to for the transistors, thewiring 13, the connection terminal 12, the wiring 15, and the like.

The liquid crystal element 710 includes a conductive layer 711, a liquidcrystal 712, and a conductive layer 713. The conductive layer 713 isprovided over the substrate 701. One or more insulating layers areprovided over the conductive layer 713, and the conductive layer 711 isprovided over the insulating layer(s). Furthermore, the liquid crystal712 is positioned between the conductive layer 711 and the substrate705. The conductive layer 713 is electrically connected to a wiring 723and functions as a common electrode. The conductive layer 711 iselectrically connected to the transistor 721 and serves as a pixelelectrode. A common potential is applied to the wiring 723.

The liquid crystal element 710 illustrated in FIG. 13 is a liquidcrystal element to which a horizontal electric field mode (for example,an FFS (Fringe Field Switching) mode) is applied. The conductive layer711 has a comb-like top surface shape or a top surface shape including aslit. In the liquid crystal element 710, the alignment state of theliquid crystal 712 is controlled by an electric field generated betweenthe conductive layer 711 and the conductive layer 713.

Furthermore, the capacitor 790 functioning as a storage capacitor isformed of a stacked-layer structure of the conductive layer 711, theconductive layer 713, and one or more insulating layers sandwichedbetween the conductive layer 711 and the conductive layer 713. Thus,another capacitor is not necessarily provided, and thus the apertureratio can be increased.

A material that transmits visible light or a material that reflectsvisible light can be used for the conductive layer 711 and theconductive layer 713. As a light-transmitting material, for example, anoxide material containing indium, zinc, tin, or the like is preferablyused. As a reflective material, for example, a material containingaluminum, silver, or the like is preferably used.

When a reflective material is used for one or both of the conductivelayer 711 and the conductive layer 713, the display device 10 b is areflective liquid crystal display device. In contrast, when alight-transmitting material is used for both of the conductive layer 711and the conductive layer 713, the display device 10 b is a transmissiveliquid crystal display device. For a reflective liquid crystal displaydevice, a polarizing plate is provided on the viewer side. By contrast,for a transmissive liquid crystal display device, a pair of polarizingplates is provided so that the liquid crystal element is placedtherebetween.

FIG. 13 shows an example of a transmissive liquid crystal displaydevice. A polarizing plate 755 and a light source 757 are provided onthe outer side of the substrate 701, and a polarizing plate 756 isprovided on the outer side of the substrate 705. The light source 757functions as a backlight.

The light-blocking layer 738 and the coloring layer 736 are provided ona surface of the substrate 705 that is on the substrate 701 side. Aninsulating layer 734 functioning as a planarization layer is provided tocover the light-blocking layer 738 and the coloring layer 736. A spacer727 is provided on a surface of the insulating layer 734 that is on thesubstrate 701 side.

The liquid crystal 712 is positioned between an alignment film 725covering the conductive layer 711 and an alignment film 726 covering theinsulating layer 734. Note that the alignment film 725 and the alignmentfilm 726 are not necessarily provided when not needed.

Although not illustrated in FIG. 13, an optical member (optical film)such as a retardation film or an anti-reflection film, a protectionfilm, an antifouling film, or the like can be provided on the outer sideof the substrate 705 as appropriate. As the anti-reflection film, an AG(Anti Glare) film, an AR (Anti Reflection) film, or the like can begiven.

As the liquid crystal 712, a thermotropic liquid crystal, alow-molecular liquid crystal, a high-molecular liquid crystal, a polymerdispersed liquid crystal (PDLC), a polymer network liquid crystal(PNLC), a ferroelectric liquid crystal, an anti-ferroelectric liquidcrystal, or the like can be used. In the case where a horizontalelectric field mode is employed, a liquid crystal exhibiting a bluephase for which an alignment film is not used may be used.

As the mode of the liquid crystal element, a TN (Twisted Nematic) mode,a VA (Vertical Alignment) mode, an IPS (In-Plane-Switching) mode, an FFSmode, an ASM (Axially Symmetric aligned Micro-cell) mode, an OCB(Optically Compensated Birefringence) mode, an ECB (ElectricallyControlled Birefringence) mode, a guest-host mode, or the like can beemployed.

In addition, a scattering liquid crystal employing a polymer dispersedliquid crystal, a polymer network liquid crystal, or the like can beused for the liquid crystal 712. At this time, monochrome image displaymay be performed without the coloring layer 736, or color display may beperformed using the coloring layer 736.

As a driving method of the liquid crystal element, a time-divisiondisplay method (also referred to as a field-sequential driving method)by which color display is performed by a successive additive colormixing method may be used. In that case, a structure without thecoloring layer 736 can be employed. In the case where the time-divisiondisplay method is employed, advantages such as the aperture ratio ofeach pixel or the resolution being increased can be obtained becausesubpixels that emit light of, for example, R (red), G (green), and B(blue), are not necessarily provided.

The display device 10 b illustrated in FIG. 13 has a structure in whichan organic insulating film functioning as a planarization layer is notprovided on a surface on which the conductive layer 711 functioning as apixel electrode or the conductive layer 713 functioning as a commonelectrode is provided. Furthermore, bottom-gate transistors, which havea relatively small number of manufacturing steps, are used as thetransistor 721 and the like included in the display device 10 b.Moreover, as described above, the wiring 13, the connection terminal 12,the wiring 15, and the like can be manufactured with steps common to themanufacturing steps of the transistors, the liquid crystal element, andthe like without special steps. With such a structure, the manufacturingcost can be reduced and the manufacturing yield can be increased, sothat a display device having high reliability can be provided at lowcost.

The above is the description of Cross-sectional structure example 2.

Components

Components such as a transistor that can be used in the display deviceare described below.

Substrate

Although there is no particular limitation on a material and the like ofthe substrate, it is necessary that the substrate have heat resistancehigh enough to withstand at least heat treatment performed later. Forexample, a single crystal semiconductor substrate or a polycrystallinesemiconductor substrate containing silicon or silicon carbide as amaterial, a compound semiconductor substrate of silicon germanium or thelike, an SOI substrate, a glass substrate, a ceramic substrate, a quartzsubstrate, a sapphire substrate, or the like may be used as thesubstrate. Alternatively, any of these substrates over which asemiconductor element is provided may be used as the substrate.

Furthermore, a flexible substrate may be used as the substrate and thedisplay device may be formed directly on the flexible substrate.Alternatively, a separation layer may be provided between the substrateand the display device. After part or the whole of the display device iscompleted over the separation layer, the separation layer can be usedfor separation from the substrate and transfer to another substrate. Inthat case, the display device can be transferred to even a substratehaving low heat resistance or a flexible substrate.

Transistor

The transistors each include a conductive layer functioning as a gateelectrode, a semiconductor layer, a conductive layer functioning as asource electrode, a conductive layer functioning as a drain electrode,and an insulating layer functioning as a gate insulating layer.

Note that there is no particular limitation on the structure of thetransistor included in the display device of one embodiment of thepresent invention. For example, a planar transistor may be employed, astaggered transistor may be employed, or an inverted staggeredtransistor may be employed. A top-gate or bottom-gate transistorstructure may be employed. Alternatively, gate electrodes may beprovided above and below a channel.

There is no particular limitation on the crystallinity of asemiconductor material used for the transistors, and any of an amorphoussemiconductor, a single crystal semiconductor, and a semiconductorhaving crystallinity other than single crystal (a microcrystallinesemiconductor, a polycrystalline semiconductor, or a semiconductorpartly including crystal regions) may be used. It is preferable that asingle crystal semiconductor or a semiconductor having crystallinity beused, in which case deterioration of the transistor characteristics canbe inhibited.

In particular, a transistor that uses a metal oxide film for asemiconductor layer where a channel is formed is described below.

As a semiconductor material used for the transistors, a metal oxidewhose energy gap is greater than or equal to 2 eV, preferably greaterthan or equal to 2.5 eV, further preferably greater than or equal to 3eV can be used. A typical example thereof is a metal oxide containingindium, and for example, a CAC-OS described later or the like can beused.

A transistor with a metal oxide having a larger band gap and a lowercarrier concentration than silicon has a low off-state current;therefore, charges stored in a capacitor that is series-connected to thetransistor can be held for a long time.

The semiconductor layer can be, for example, a film represented by anIn-M-Zn-based oxide that contains indium, zinc, and M (M is a metal suchas aluminum, titanium, gallium, germanium, yttrium, zirconium,lanthanum, cerium, tin, neodymium, or hafnium).

In the case where a metal oxide that constitutes the semiconductor layeris an In-M-Zn-based oxide, it is preferable that the atomic ratio ofmetal elements in a sputtering target used to deposit an In-M-Zn oxidesatisfy In≥M and Zn≥M. The atomic ratio between metal elements in such asputtering target is preferably, for example, In:M:Zn=1:1:1,In:M:Zn=1:1:1.2, In:M:Zn=3:1:2, In:M:Zn=4:2:3, In:M:Zn=4:2:4.1,In:M:Zn=5:1:6, In:M:Zn=5:1:7, or In:M:Zn=5:1:8. Note that the atomicratio between metal elements in the formed semiconductor layer may varyfrom the above atomic ratio between metal elements in the sputteringtarget in a range of ±40%.

A metal oxide film with a low carrier concentration is used as thesemiconductor layer. For example, for the semiconductor layer, a metaloxide whose carrier concentration is lower than or equal to 1×10¹⁷ cm⁻³,preferably lower than or equal to 1×10¹⁵ cm⁻³, further preferably lowerthan or equal to 1×10¹³ cm⁻³, still further preferably lower than orequal to 1×10¹¹ cm⁻³, even further preferably lower than 1×10¹⁰ cm⁻³,and higher than or equal to 1×10⁻⁹ cm⁻³ can be used. Such a metal oxideis referred to as a highly purified intrinsic or substantially highlypurified intrinsic metal oxide. The oxide semiconductor has a lowdensity of defect states and thus can be regarded as a metal oxidesemiconductor having stable characteristics.

Note that, without limitation to these, an oxide semiconductor with anappropriate composition may be used in accordance with requiredsemiconductor characteristics and electrical characteristics (e.g.,field-effect mobility and threshold voltage) of the transistor. Inaddition, to obtain the required semiconductor characteristics of thetransistor, it is preferable that the carrier concentration, impurityconcentration, defect density, atomic ratio between a metal element andoxygen, interatomic distance, density, and the like of the semiconductorlayer be set to be appropriate.

When silicon or carbon, which is one of the Group 14 elements, iscontained in the metal oxide that constitutes the semiconductor layer,oxygen vacancies are increased, and the semiconductor layer becomesn-type. Thus, the concentration of silicon or carbon (measured bysecondary ion mass spectrometry) in the semiconductor layer is set to2×10¹⁸ atoms/cm³ or lower, preferably 2×10¹⁷ atoms/cm³ or lower.

Alkali metal and alkaline earth metal might generate carriers whenbonded to a metal oxide, in which case the off-state current of thetransistor might be increased. Thus, the concentration of alkali metalor alkaline earth metal in the semiconductor layer is set to lower thanor equal to 1×10¹⁸ atoms/cm³, preferably lower than or equal to 2×10¹⁶atoms/cm³.

Furthermore, when nitrogen is contained in the metal oxide thatconstitutes the semiconductor layer, electrons serving as carriers aregenerated and the carrier concentration is increased, so that thesemiconductor layer easily becomes n-type. As a result, a transistorusing a metal oxide that contains nitrogen is likely to have normally-oncharacteristics. Therefore, the concentration of nitrogen in thesemiconductor layer, which is measured by secondary ion massspectrometry, is preferably set to lower than or equal to 5×10¹⁸atoms/cm³.

Oxide semiconductors are classified into a single crystal oxidesemiconductor and a non- single-crystal oxide semiconductor. Examples ofthe non-single-crystal oxide semiconductor include a CAAC-OS(c-axis-aligned crystalline oxide semiconductor), a polycrystallineoxide semiconductor, an nc-OS (nanocrystalline oxide semiconductor), anamorphous-like oxide semiconductor (a-like OS), and an amorphous oxidesemiconductor.

Note that the non-single-crystal oxide semiconductor can be suitablyused for a semiconductor layer of a transistor disclosed in oneembodiment of the present invention. As the non-single-crystal oxidesemiconductor, the nc-OS or the CAAC-OS can be suitably used.

The semiconductor layer may be a mixed film including two or more of aregion of a CAAC-OS, a region of a polycrystalline oxide semiconductor,a region of an nc-OS, a region of an amorphous-like oxide semiconductor,and a region of an amorphous oxide semiconductor. The mixed film has,for example, a single-layer structure or a layered structure includingtwo or more of the foregoing regions in some cases.

A CAC-OS (Cloud-Aligned Composite oxide semiconductor) is preferablyused for a semiconductor layer of a transistor disclosed in oneembodiment of the present invention. The use of the CAC-OS allows thetransistor to have high electrical characteristics or high reliability.

A CAAC (c-axis aligned crystal) is described below. A CAAC refers to anexample of a crystal structure.

The CAAC structure is a crystal structure of a thin film or the likethat has a plurality of nanocrystals (crystal regions having a maximumdiameter of less than 10 nm), characterized in that the nanocrystalshave c-axis alignment in a particular direction and are not aligned butcontinuously connected in the a-axis and b-axis directions withoutforming a grain boundary. In particular, a thin film having the CAACstructure is characterized in that the c-axes of nanocrystals are likelyto be aligned in a film thickness direction, a normal direction of asurface where the thin film is formed, or a normal direction of asurface of the thin film.

A CAAC-OS (Oxide Semiconductor) is an oxide semiconductor with highcrystallinity. By contrast, in the CAAC-OS, it can be said that areduction in electron mobility due to the crystal grain boundary is lesslikely to occur because a clear crystal grain boundary cannot beobserved. Moreover, since the crystallinity of an oxide semiconductormight be decreased by entry of impurities, formation of defects, or thelike, the CAAC-OS can be regarded as an oxide semiconductor that hassmall amounts of impurities and defects (oxygen vacancies or the like).Thus, an oxide semiconductor including a CAAC-OS is physically stable.Therefore, the oxide semiconductor including the CAAC-OS is resistant toheat and has high reliability.

Here, in crystallography, in a unit cell formed with three axes (crystalaxes) of the a-axis, the b-axis, and the c-axis, a specific axis isgenerally taken as the c-axis. In particular, in the case of a crystalhaving a layered structure, two axes parallel to the plane direction ofa layer are regarded as the a-axis and the b-axis and an axisintersecting with the layer is regarded as the c-axis in general.Typical examples of such a crystal having a layered structure includegraphite, which is classified as a hexagonal system. In a unit cell ofgraphite, the a-axis and the b-axis are parallel to a cleavage plane andthe c-axis is orthogonal to the cleavage plane. For example, an InGaZnO₄crystal having a YbFe₂O₄ type crystal structure, which is a layeredstructure, can be classified as a hexagonal system, and in a unit cellthereof, the a-axis and the b-axis are parallel to the plane directionof a layer and the c-axis is orthogonal to the layer (i.e., the a-axisand the b-axis).

In an image observed with a TEM, crystal parts cannot be found clearlyin an oxide semiconductor film having a microcrystalline structure (amicrocrystalline oxide semiconductor film) in some cases. In most cases,the size of a crystal part included in the microcrystalline oxidesemiconductor film is greater than or equal to 1 nm and less than orequal to 100 nm, or greater than or equal to 1 nm and less than or equalto 10 nm. In particular, an oxide semiconductor film including ananocrystal (nc) that is a microcrystal with a size greater than orequal to 1 nm and less than or equal to 10 nm, or greater than or equalto 1 nm and less than or equal to 3 nm is referred to as an nc-OS(nanocrystalline Oxide Semiconductor) film. In an image observed with aTEM, for example, a crystal grain boundary cannot be found clearly inthe nc-OS film in some cases.

In the nc-OS film, a microscopic region (for example, a region with asize greater than or equal to 1 nm and less than or equal to 10 nm, inparticular, a region with a size greater than or equal to 1 nm and lessthan or equal to 3 nm) has a periodic atomic arrangement. Furthermore,there is no regularity of crystal orientation between different crystalparts in the nc-OS film. Thus, the orientation in the whole film is notobserved. Accordingly, in some cases, the nc-OS film cannot bedistinguished from an amorphous oxide semiconductor film depending on ananalysis method. For example, when the nc-OS film is subjected tostructural analysis by an out-of-plane method with an XRD apparatususing an X-ray having a diameter larger than the size of a crystal part,a peak that shows a crystal plane does not appear. Furthermore, adiffraction pattern like a halo pattern is observed when the nc-OS filmis subjected to electron diffraction (also referred to as selected-areaelectron diffraction) using an electron beam with a probe diameter(e.g., 50 nm or larger) larger than the diameter of a crystal part.Meanwhile, in some cases, a circular (ring-like) region with highluminance is observed in an electron diffraction pattern (also referredto as nanobeam electron diffraction pattern) of the nc-OS film, which isobtained using an electron beam with a probe diameter (e.g., 1 nm orlarger and 30 nm or smaller) close to or smaller than the diameter of acrystal part, and spots are observed in the ring-like region.

The nc-OS film has a lower density of defect states than an amorphousoxide semiconductor film. Note that there is no regularity of crystalorientation between different crystal parts in the nc-OS film. Thus, thenc-OS film has a higher density of defect states than the CAAC-OS film.Accordingly, the nc-OS film has a higher carrier concentration andhigher electron mobility than the CAAC-OS film in some cases. Therefore,a transistor using the nc-OS film may have high field-effect mobility.

The nc-OS film can be formed at a smaller oxygen flow rate ratio information than the CAAC-OS film. The nc-OS film can also be formed at alower substrate temperature in formation than the CAAC-OS film. Forexample, the nc-OS film can be formed at a relatively low substratetemperature (e.g., a temperature of 130° C. or lower) or without heatingof the substrate and thus is suitable for the case of using a largeglass substrate, a resin substrate, or the like, and productivity can beincreased.

An example of a crystal structure of a metal oxide is described. A metaloxide that is formed by a sputtering method using an In—Ga—Zn oxidetarget (In:Ga:Zn=4:2:4.1 [atomic ratio]) at a substrate temperaturehigher than or equal to 100° C. and lower than or equal to 130° C. islikely to have either the nc (nano crystal) structure or the CAACstructure, or a structure in which both structures are mixed. Bycontrast, a metal oxide formed at a substrate temperature set at roomtemperature (R.T.) is likely to have the nc structure. Note that roomtemperature (R.T.) here also includes a temperature in the case where asubstrate is not heated intentionally.

Composition of CAC-OS

The composition of a CAC (Cloud-Aligned Composite)-OS that can be usedin a transistor disclosed in one embodiment of the present invention isdescribed below.

A CAC-OS refers to one composition of a material in which elementsconstituting a metal oxide are unevenly distributed with a size greaterthan or equal to 0.5 nm and less than or equal to 10 nm, preferablygreater than or equal to 1 nm and less than or equal to 2 nm, or asimilar size, for example. Note that a state in which one or more metalelements are unevenly distributed and regions including the metalelement(s) are mixed with a size greater than or equal to 0.5 nm andless than or equal to 10 nm, preferably greater than or equal to 1 nmand less than or equal to 2 nm, or a similar size in a metal oxide ishereinafter referred to as a mosaic pattern or a patch-like pattern.

Note that the metal oxide preferably contains at least indium. Inparticular, indium and zinc are preferably contained. In addition, oneor more of aluminum, gallium, yttrium, copper, vanadium, beryllium,boron, silicon, titanium, iron, nickel, germanium, zirconium,molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten,magnesium, and the like may be contained.

For example, of the CAC-OS, an In—Ga—Zn oxide with the CAC composition(such an In—Ga—Zn oxide may be particularly referred to as CAC-IGZO) hasa composition in which materials are separated into indium oxide(InO_(X1), where X1 is a real number greater than 0) or indium zincoxide (In_(X2)Zn_(Y2)O_(Z2), where X2, Y2, and Z2 are real numbersgreater than 0), and gallium oxide (GaO_(X3), where X3 is a real numbergreater than 0) or gallium zinc oxide (Ga_(X4)Zn_(Y4)O_(Z4), where X4,Y4, and Z4 are real numbers greater than 0), and a mosaic pattern isformed. Then, InO_(X1) or In_(X2)Zn_(Y2)O_(Z2) forming the mosaicpattern is evenly distributed in the film. This composition is alsoreferred to as a cloud-like composition.

That is, the CAC-OS is a composite metal oxide having a composition inwhich a region including GaO_(X3) as a main component and a regionincluding In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component aremixed. Note that in this specification, when the atomic ratio of In toan element M in a first region is greater than the atomic ratio of In toan element M in a second region, for example, the first region isdescribed as having higher In concentration than the second region.

Note that a compound containing In, Ga, Zn, and O is also known as IGZO.Typical examples of IGZO include a crystalline compound represented byInGaO₃(ZnO)_(m1) (m1 is a natural number) and a crystalline compoundrepresented by In_((1+x0))Ga_((1−x0))O₃(ZnO)_(m0) (−1≤x0≤1; m0 is agiven number).

The above crystalline compounds have a single crystal structure, apolycrystalline structure, or a CAAC structure. Note that the CAACstructure is a crystal structure in which a plurality of IGZOnanocrystals have c-axis alignment and are connected in the a-b planedirection without alignment.

Meanwhile, the CAC-OS relates to the material composition of a metaloxide. In a material composition of a CAC-OS containing In, Ga, Zn, andO, nanoparticle regions containing Ga as a main component are observedin part of the CAC-OS and nanoparticle regions containing In as a maincomponent are observed in part thereof. These nanoparticle regions arerandomly dispersed to form a mosaic pattern. Therefore, the crystalstructure is a secondary element for the CAC-OS.

Note that in the CAC-OS, a layered structure including two or more filmswith different atomic ratios is not included. For example, a two-layerstructure of a film containing In as a main component and a filmcontaining Ga as a main component is not included.

A boundary between the region containing GaO_(X3) as a main componentand the region containing In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a maincomponent is not clearly observed in some cases.

In the case where one or more of aluminum, yttrium, copper, vanadium,beryllium, boron, silicon, titanium, iron, nickel, germanium, zirconium,molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten,magnesium, and the like are contained instead of gallium in a CAC-OS,nanoparticle regions containing the selected metal element(s) as a maincomponent(s) are observed in part of the CAC-OS and nanoparticle regionscontaining In as a main component are observed in part of the CAC-OS,and these nanoparticle regions are randomly dispersed to form a mosaicpattern in the CAC-OS.

The CAC-OS can be formed by a sputtering method under a condition wherea substrate is not heated intentionally, for example. Moreover, in thecase of forming the CAC-OS by a sputtering method, any one or moreselected from an inert gas (typically, argon), an oxygen gas, and anitrogen gas are used as a deposition gas. The flow rate of the oxygengas to the total flow rate of the deposition gas in deposition ispreferably as low as possible, for example, the flow rate of the oxygengas is higher than or equal to 0% and lower than 30%, preferably higherthan or equal to 0% and lower than or equal to 10%.

The CAC-OS is characterized in that a clear peak is not observed whenmeasurement is conducted using a θ/2θ scan by an out-of-plane method,which is an X-ray diffraction (XRD) measurement method. That is, it isfound by the X-ray diffraction measurement that there are no alignmentin the a-b plane direction and no alignment in the c-axis direction inthe measured areas.

In an electron diffraction pattern of the CAC-OS which is obtained byirradiation with an electron beam with a probe diameter of 1 nm (alsoreferred to as a nanometer-sized electron beam), a ring-like region withhigh luminance and a plurality of bright spots in the ring-like regionare observed. Therefore, the electron diffraction pattern indicates thatthe crystal structure of the CAC-OS includes an nc (nano-crystal)structure with no alignment in the plan-view direction and thecross-sectional direction.

Moreover, for example, it can be checked by EDX mapping obtained usingenergy dispersive X-ray spectroscopy (EDX) that the CAC-OS in theIn—Ga—Zn oxide has a composition in which regions including GaO_(X3) asa main component and regions including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1)as a main component are unevenly distributed and mixed.

The CAC-OS has a structure different from that of an IGZO compound inwhich metal elements are evenly distributed, and has characteristicsdifferent from those of the IGZO compound. That is, in the CAC-OS, theregion containing GaO_(X3) or the like as a main component and theregion containing In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main componentare separated to form a mosaic pattern.

The conductivity of the region containing In_(X2)Zn_(Y2)O_(Z2) orInO_(X1) as a main component is higher than that of the regioncontaining GaO_(X3) or the like as a main component. In other words,when carriers flow through the regions including In_(X2)Zn_(Y2)O_(Z2) orInO_(X1) as a main component, the conductivity of a metal oxide isexhibited. Accordingly, when the regions including In_(X2)Zn_(Y2)O_(Z2)or InO_(X1) as a main component are distributed in a metal oxide like acloud, high field-effect mobility (μ) can be achieved.

By contrast, the insulating property of the region containing GaO_(X3)or the like as a main component is superior to that of the regioncontaining In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component. Inother words, when regions including GaO_(X3) or the like as a maincomponent are distributed in a metal oxide, leakage current can beinhibited and favorable switching operation can be achieved.

Accordingly, when a CAC-OS is used for a semiconductor element, theinsulating property derived from GaO_(X3) or the like and theconductivity derived from In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) complementeach other, whereby high on-state current (I_(on)) and high field-effectmobility (μ) can be achieved.

A semiconductor element using a CAC-OS has high reliability. Thus, theCAC-OS is suitably used in a variety of semiconductor devices typifiedby a display.

Since a transistor including a CAC-OS in a semiconductor layer has highfield-effect mobility and high driving capability, the use of thetransistor in a driver circuit, typically a scan line driver circuitthat generates a gate signal, enables a display device with a narrowframe width (also referred to as a narrow bezel) to be provided.Furthermore, with the use of the transistor in a signal line drivercircuit that is included in a display device (particularly in ademultiplexer connected to an output terminal of a shift registerincluded in a signal line driver circuit), the display device connectedto less number of wirings can be provided.

Furthermore, unlike a transistor including low-temperature polysilicon,the transistor including a CAC-OS in the semiconductor layer does notneed a laser crystallization step. Thus, the manufacturing cost of adisplay device can be reduced, even when the display device is formedusing a large substrate. In addition, the transistor including a CAC-OSin the semiconductor layer is preferably used for a driver circuit and adisplay unit in a large display device having high resolution such asultra-high definition (“4K resolution”, “4K2K”, and “4K”) or super highdefinition (“8K resolution”, “8K4K”, and “8K”), in which case writingcan be performed in a short time and display defects can be reduced.

Alternatively, silicon may be used for a semiconductor in which achannel of a transistor is formed. As the silicon, amorphous silicon maybe used but silicon having crystallinity is preferably used. Forexample, microcrystalline silicon, polycrystalline silicon, orsingle-crystal silicon are preferably used. In particular,polycrystalline silicon can be formed at a temperature lower than thatfor single crystal silicon and has higher field-effect mobility andhigher reliability than amorphous silicon.

Conductive Layer

Examples of materials that can be used for conductive layers of avariety of wirings and electrodes and the like included in the displaydevice in addition to a gate, a source, and a drain of a transistorinclude metals such as aluminum, titanium, chromium, nickel, copper,yttrium, zirconium, molybdenum, silver, tantalum, and tungsten and analloy containing such a metal as its main component. A single-layerstructure or stacked-layer structure including a film containing any ofthese materials can be used. For example, a single-layer structure of analuminum film containing silicon, a two-layer structure in which analuminum film is stacked over a titanium film, a two-layer structure inwhich an aluminum film is stacked over a tungsten film, a two-layerstructure in which a copper film is stacked over acopper-magnesium-aluminum alloy film, a two-layer structure in which acopper film is stacked over a titanium film, a two-layer structure inwhich a copper film is stacked over a tungsten film, a three-layerstructure in which an aluminum film or a copper film is stacked over atitanium film or a titanium nitride film and a titanium film or atitanium nitride film is formed thereover, a three-layer structure inwhich an aluminum film or a copper film is stacked over a molybdenumfilm or a molybdenum nitride film and a molybdenum film or a molybdenumnitride film is formed thereover, and the like can be given. Note thatan oxide such as indium oxide, tin oxide, or zinc oxide may be used.Furthermore, copper containing manganese is preferably used because itincreases controllability of a shape by etching.

Insulating Layer

Examples of an insulating material that can be used for the insulatinglayers include, in addition to a resin such as acrylic or epoxy and aresin having a siloxane bond, an inorganic insulating material such assilicon oxide, silicon oxynitride, silicon nitride oxide, siliconnitride, or aluminum oxide.

The light-emitting element is preferably provided between a pair ofinsulating films with low water permeability. In that case, impuritiessuch as water can be inhibited from entering the light-emitting element,and thus a decrease in device reliability can be inhibited.

Examples of the insulating film with low water permeability include afilm containing nitrogen and silicon, such as a silicon nitride film anda silicon nitride oxide film, and a film containing nitrogen andaluminum, such as an aluminum nitride film. Alternatively, a siliconoxide film, a silicon oxynitride film, an aluminum oxide film, or thelike may be used.

For example, the moisture vapor transmission rate of the insulating filmwith low water permeability is lower than or equal to 1×10⁻⁵[g/(m²·day)], preferably lower than or equal to 1×10⁻⁶ [g/(m²·day)],further preferably lower than or equal to 1×10⁻⁷ [g/(m²·day)], stillfurther preferably lower than or equal to 1×10⁻⁸ [g/(m²·day)].

The above is the description of the components.

At least part of the structure examples, the drawings correspondingthereto, and the like exemplified in this embodiment can be implementedin combination with the other structure examples, the other drawings,and the like as appropriate.

At least part of this embodiment can be implemented in combination withthe other embodiments described in this specification as appropriate.

Embodiment 2

The second wiring (the wiring 14) described as an example in Embodiment1 can be used not only for a display device but also for a variety ofsemiconductor devices. That is, the second wiring can be favorably usedalso for a semiconductor circuit that is provided over a single crystalsubstrate, a glass substrate, or a film substrate and does not have adisplay function.

A TEG (Test Element Group) is known as an element for evaluatingelectrical characteristics and the like of a fabricated element, afabricated circuit, or the like in research and development, productionmanagement, and the like of a variety of semiconductor devices includingdisplay devices. Such a TEG includes a terminal that is to be touched bya measurement probe. In many cases, the terminal has a sufficientlylarger area than an element to be measured and thus is easily influencedby ESD. Thus, the electrical characteristics of the element to bemeasured are changed by the influence of ESD in some cases.

In this embodiment, an example in the case where the wiring 14 describedas an example in Embodiment 1 is used for a TEG is described.

FIG. 14A is a schematic top view of a TEG 100 a. The TEG 100 a includesan element to be measured 101, a plurality of terminals 102, wirings103, and the wiring 14.

As the element to be measured 101, a variety of elements or a circuitcan be used. For example, a transistor, a resistor, a capacitor, awiring, or a circuit including one or more of these can be given.Furthermore, as the element to be measured 101, a variety of elementsfor measurement purposes, such as an evaluation element for contactresistance and an element for evaluating a breakdown voltage, can beused.

Here, four terminals 102 electrically connected to the element to bemeasured 101. For example, in the case where a transistor is used as theelement to be measured 101, the four terminals 102 correspond toterminals electrically connected to a first gate electrode, a secondgate electrode, a source electrode, and a drain electrode of thetransistor through the wirings 103.

The wiring 14 is electrically connected to the four terminals 102. Here,the wiring 14 is cut by a cut line 120 illustrated in FIG. 14A, so thatthe four terminals 102 can be electrically isolated. As illustrated inFIG. 14A, to make all of the terminals 102 electrically isolated byone-time cutting, it is preferable that parts of the wiring 14 bearranged parallel to each other (also referred to as a comb-likeportion) in the top surface shape. Furthermore, although the example inwhich the wiring 14 has a straight shape is shown here, for example, atleast part of the wiring 14 may have a gentle meandering shape, an Sshape, or a plurality of S shapes connected to each other (also referredto as a pleated shape).

The cutting of the wiring 14 is preferably performed right before themeasurement. Although the method for cutting the wiring 14 is notparticularly limited, a laser cutter can be favorably used.

When the plurality of terminals 102 included in the TEG 100 a areelectrically connected to each other by the wiring 14 until right beforethe measurement, an influence by ESD generated due to electrification ofa substrate during the manufacturing steps or a manufactured substrateis reduced, so that a breakdown of the element to be measured 101 or achange in electrical characteristics can be favorably inhibited.

FIG. 14B shows a TEG 100 b in which two out of the four terminals 102are electrically connected to each other by the wiring 14. Like this, astructure may be used in which not all the terminals 102 areelectrically connected but only the terminals 102 that are electricallyconnected to electrodes or the like having a low withstand voltage inthe element to be measured 101 are selected and electrically connectedto each other by the wiring 14 depending on the structure of the elementto be measured 101.

FIG. 14C shows a TEG 100 c including the element to be measured 101having two terminals, as an example. FIG. 14D shows an example of a TEG100 d including the element to be measured 101 having three terminals.

FIG. 14E shows an example of a TEG 100 c including a wiring 14 p thatelectrically connects two of the four terminals 102 and a wiring 14 qthat electrically connects the other two. As illustrated in FIG. 14E, inthe case where two or more wirings 14 that are electrically insulatedare included, the top surface shape in which the wirings 14 can be cutat a time is preferable.

Note that the number of the terminals 102 is not limited to the above,and five or more terminals may be included depending on the structure ofthe element to be measured 101.

At least part of this embodiment can be implemented in combination withthe other embodiments described in this specification as appropriate.

Embodiment 3

In this embodiment, a display device that includes the semiconductordevice of one embodiment of the present invention is described withreference to FIG. 15.

A display device illustrated in FIG. 15A includes a pixel portion 502, adriver circuit portion 504, protection circuits 506, and a terminalportion 507. Note that a structure in which the protection circuits 506are not provided may be employed.

The transistor of one embodiment of the present invention can be used astransistors included in the pixel portion 502 and the driver circuitportion 504. The transistor of one embodiment of the present inventionmay also be used in the protection circuits 506.

The pixel portion 502 includes a plurality of pixel circuits 501 thatdrive a plurality of display elements arranged in X rows and Y columns(X and Y each independently represent a natural number of 2 or more).

The driver circuit portion 504 includes driver circuits such as a gatedriver 504 a that outputs a scanning signal to gate lines GL_1 to GL_Xand a source driver 504 b that supplies a data signal to data lines DL_1to DL_Y. The gate driver 504 a includes at least a shift register. Thesource driver 504 b is formed using a plurality of analog switches, forexample. Alternatively, the source driver 504 b may be formed using ashift register or the like.

The terminal portion 507 refers to a portion provided with terminals forinputting power, control signals, image signals, and the like to thedisplay device from external circuits.

The protection circuit 506 is a circuit that, when a potential out of acertain range is applied to a wiring to which the protection circuit 506is connected, establishes continuity between the wiring and anotherwiring. The protection circuit 506 illustrated in FIG. 15A is connectedto a variety of wirings such as the gate lines GL that are wiringsbetween the gate driver 504 a and the pixel circuits 501 and the datalines DL that are wirings between the source driver 504 b and the pixelcircuits 501, for example. Note that the protection circuits 506 arehatched in FIG. 15A to distinguish the protection circuits 506 from thepixel circuits 501.

The gate driver 504 a and the source driver 504 b may be provided over asubstrate over which the pixel portion 502 is provided, or a substratewhere a gate driver circuit or a source driver circuit is separatelyformed (e.g., a driver circuit board formed using a single crystalsemiconductor or a polycrystalline semiconductor) may be mounted on thesubstrate by COG or TAB (Tape Automated Bonding).

The plurality of pixel circuits 501 illustrated in FIG. 15A can have aconfiguration illustrated in FIG. 15B or FIG. 15C, for example.

The pixel circuit 501 illustrated in FIG. 15B includes a liquid crystalelement 570, a transistor 550, and a capacitor 560. The data line DL_n,the gate line GL_m, a potential supply line VL, and the like areconnected to the pixel circuit 501.

The potential of one of a pair of electrodes of the liquid crystalelement 570 is set appropriately in accordance with the specificationsof the pixel circuit 501. The alignment state of the liquid crystalelement 570 is set depending on written data. Note that a commonpotential may be supplied to one of the pair of electrodes of the liquidcrystal element 570 included in each of the plurality of pixel circuits501. Moreover, a different potential may be supplied to one of the pairof electrodes of the liquid crystal element 570 of the pixel circuit 501in each row.

The pixel circuit 501 illustrated in FIG. 15C includes a transistor 552and a transistor 554, a capacitor 562, and a light-emitting element 572.The data line DL_n, the gate line GL_m, a potential supply line VL_a, apotential supply line VL_b, and the like are connected to the pixelcircuit 501.

Note that a high power supply potential VDD is supplied to one of thepotential supply line VL_a and the potential supply line VL_b, and a lowpower supply potential VSS is supplied to the other. Current flowingthrough the light-emitting element 572 is controlled in accordance witha potential applied to a gate of the transistor 554, whereby theluminance of light emitted from the light-emitting element 572 iscontrolled.

At least part of the structure examples, the drawings correspondingthereto, and the like exemplified in this embodiment can be implementedin combination with the other structure examples, the other drawings,and the like as appropriate.

At least part of this embodiment can be implemented in combination withthe other embodiments described in this specification as appropriate.

Embodiment 4

A pixel circuit including a memory for correcting gray levels displayedby pixels and a display device including the pixel circuit are describedbelow. The transistor described in

Embodiment 1 can be used as a transistor used in the pixel circuitdescribed below.

Circuit Configuration

FIG. 16A is a circuit diagram of a pixel circuit 400. The pixel circuit400 includes a transistor M1, a transistor M2, a capacitor C1, and acircuit 401. A wiring S1, a wiring S2, a wiring G1, and a wiring G2 areconnected to the pixel circuit 400.

In the transistor M1, a gate is connected to the wiring G1, one of asource and a drain is connected to the wiring S1, and the other isconnected to one electrode of the capacitor C1. In the transistor M2, agate is connected to the wiring G2, one of a source and a drain isconnected to the wiring S2, and the other is connected to the otherelectrode of the capacitor C1 and the circuit 401.

The circuit 401 is a circuit including at least one display element. Anyof a variety of elements can be used as the display element, andtypically, a light-emitting element such as an organic EL element or anLED element, a liquid crystal element, a MEMS (Micro Electro MechanicalSystems) element, or the like can be used.

A node connecting the transistor M1 and the capacitor C1 is denoted as anode N1, and a node connecting the transistor M2 and the circuit 401 isdenoted as a node N2.

In the pixel circuit 400, the potential of the node N1 can be retainedwhen the transistor M1 is turned off. The potential of the node N2 canbe retained when the transistor M2 is turned off. When a predeterminedpotential is written to the node N1 through the transistor M1 with thetransistor M2 being in an off state, the potential of the node N2 can bechanged in accordance with displacement of the potential of the node N1owing to capacitive coupling through the capacitor C1.

Here, the transistor using an oxide semiconductor, which is described inEmbodiment 1, can be used as one or both of the transistor M1 and thetransistor M2. Accordingly, owing to an extremely low off-state current,the potentials of the node N1 and the node N2 can be retained for a longtime. Note that in the case where the period in which the potential ofeach node is retained is short (specifically, the case where the framefrequency is higher than or equal to 30 Hz, for example), a transistorusing a semiconductor such as silicon may be used.

Driving Method Example

Next, an example of a method for operating the pixel circuit 400 isdescribed with reference to FIG. 16B. FIG. 16B is a timing chart of theoperation of the pixel circuit 400. Note that for simplification ofdescription, the influence of various kinds of resistance such as wiringresistance, parasitic capacitance of a transistor, a wiring, or thelike, the threshold voltage of the transistor, and the like is not takeninto account here.

In the operation shown in FIG. 16B, one frame period is divided into aperiod T1 and a period T2. The period T1 is a period in which apotential is written to the node N2, and the period T2 is a period inwhich a potential is written to the node N1.

Period T1

In the period T1, a potential for turning on the transistor is suppliedto both the wiring G1 and the wiring G2. In addition, a potentialV_(ref) that is a fixed potential is supplied to the wiring S1, and afirst data potential V_(w) is supplied to the wiring S2.

The potential V_(ref) is supplied from the wiring S1 to the node N1through the transistor M1. The first data potential V_(w) is suppliedfrom the wiring S2 to the node N2 through the transistor M2.Accordingly, a potential difference V_(w)−V_(ref) is retained in thecapacitor C1.

Period T2

Next, in the period T2, a potential for turning on the transistor M1 issupplied to the wiring G1, and a potential for turning off thetransistor M2 is supplied to the wiring G2. A second data potentialV_(data) is supplied to the wiring S1. The wiring S2 may be suppliedwith a predetermined constant potential or brought into a floatingstate.

The second data potential V_(data) is supplied from the wiring S1 to thenode N1 through the transistor M1. At this time, capacitive coupling dueto the capacitor C1 changes the potential of the node N2 in accordancewith the second data potential V_(data) by a potential dV. That is, apotential that is the sum of the first data potential V_(w) and thepotential dV is input to the circuit 401. Note that although dV is shownas a positive value in FIG. 16B, dV may be a negative value. That is,the second data potential V_(data) may be lower than the potentialV_(ref).

Here, the potential dV is roughly determined by the capacitance of thecapacitor C1 and the capacitance of the circuit 401. When thecapacitance of the capacitor C1 is sufficiently larger than thecapacitance of the circuit 401, the potential dV is a potential close tothe second data potential V_(data).

In the above manner, the pixel circuit 400 can generate a potential tobe supplied to the circuit 401 including the display element, bycombining two kinds of data signals; hence, a gray level can becorrected in the pixel circuit 400.

The pixel circuit 400 can also generate a potential exceeding themaximum potential that can be supplied to the wiring S1 and the wiringS2. For example, in the case where a light-emitting element is used,high-dynamic range (HDR) display or the like can be performed. In thecase where a liquid crystal element is used, overdriving or the like canbe achieved.

APPLICATION EXAMPLES Example Using Liquid Crystal Element

A pixel circuit 400LC illustrated in FIG. 16C includes a circuit 401LC.The circuit 401LC includes a liquid crystal element LC and a capacitorC2.

In the liquid crystal element LC, one electrode is connected to the nodeN2 and one electrode of the capacitor C2, and the other electrode isconnected to a wiring supplied with a potential V_(com2). The otherelectrode of the capacitor C2 is connected to a wiring supplied with apotential V_(com1).

The capacitor C2 functions as a storage capacitor. Note that thecapacitor C2 can be omitted when not needed.

In the pixel circuit 400LC, a high voltage can be supplied to the liquidcrystal element LC; thus, high-speed display can be performed byoverdriving or a liquid crystal material with a high driving voltage canbe employed, for example. Moreover, by supply of a correction signal tothe wiring S1 or the wiring S2, a gray level can be corrected inaccordance with the operating temperature, the deterioration state ofthe liquid crystal element LC, or the like.

Example Using Light-Emitting Element

A pixel circuit 400EL illustrated in FIG. 16D includes a circuit 401EL.The circuit 401EL includes a light-emitting element EL, a transistor M3,and the capacitor C2.

In the transistor M3, a gate is connected to the node N2 and oneelectrode of the capacitor C2, one of a source and a drain is connectedto a wiring supplied with a potential V_(H), and the other is connectedto one electrode of the light-emitting element EL. The other electrodeof the capacitor C2 is connected to a wiring supplied with a potentialV_(com). The other electrode of the light-emitting element EL isconnected to a wiring supplied with a potential V_(L).

The transistor M3 has a function of controlling a current to be suppliedto the light-emitting element EL. The capacitor C2 functions as astorage capacitor. The capacitor C2 can be omitted when not needed.

Note that although the structure in which the anode side of thelight-emitting element EL is connected to the transistor M3 is describedhere, the transistor M3 may be connected to the cathode side. In thatcase, the values of the potential V_(H) and the potential V_(L) can beappropriately changed.

In the pixel circuit 400EL, a large amount of current can flow throughthe light-emitting element EL when a high potential is applied to thegate of the transistor M3, which enables HDR display, for example.Moreover, a variation in the electrical characteristics of thetransistor M3 and the light-emitting element EL can be corrected bysupply of a correction signal to the wiring S1 or the wiring S2.

Note that the configuration is not limited to the circuits shown in FIG.16C and FIG. 16D, and a configuration to which a transistor, acapacitor, or the like is further added may be employed.

At least part of this embodiment can be implemented in combination withthe other embodiments described in this specification as appropriate.

Embodiment 5

In this embodiment, a display module that can be fabricated using oneembodiment of the present invention is described.

In a display module 6000 illustrated in FIG. 17A, a display device 6006to which an FPC 6005 is connected, a frame 6009, a printed circuit board6010, and a battery 6011 are provided between an upper cover 6001 and alower cover 6002.

A display device fabricated using one embodiment of the presentinvention can be used as the display device 6006, for example. With thedisplay device 6006, a display module with extremely low powerconsumption can be achieved.

The shape and size of the upper cover 6001 and the lower cover 6002 canbe changed as appropriate in accordance with the size of the displaydevice 6006.

The display device 6006 may have a function of a touch panel.

The frame 6009 may have a function of protecting the display device6006, a function of blocking electromagnetic waves generated by theoperation of the printed circuit board 6010, a function of a heatdissipation plate, or the like.

The printed circuit board 6010 includes a power supply circuit, a signalprocessing circuit for outputting a video signal and a clock signal, abattery control circuit, and the like.

FIG. 17B is a schematic cross-sectional view of the display module 6000having an optical touch sensor.

The display module 6000 includes a light-emitting portion 6015 and alight-receiving portion 6016 that are provided on the printed circuitboard 6010. Furthermore, a pair of light guide portions (a light guideportion 6017 a and a light guide portion 6017 b) is provided in a regionsurrounded by the upper cover 6001 and the lower cover 6002.

The display device 6006 overlaps the printed circuit board 6010 and thebattery 6011 with the frame 6009 therebetween. The display device 6006and the frame 6009 are fixed to the light guide portion 6017 a and thelight guide portion 6017 b.

Light 6018 emitted from the light-emitting portion 6015 travels over thedisplay device 6006 through the light guide portion 6017 a and reachesthe light-receiving portion 6016 through the light guide portion 6017 b.For example, blocking of the light 6018 by a sensing target such as afinger or a stylus enables detection of touch operation.

A plurality of light-emitting portions 6015 are provided along twoadjacent sides of the display device 6006, for example. A plurality oflight-receiving portions 6016 are provided at the positions on theopposite side of the light-emitting portions 6015. Accordingly,information about the position of touch operation can be obtained.

As the light-emitting portion 6015, a light source such as an LEDelement can be used, for example, and it is particularly preferable touse a light source emitting infrared rays. As the light-receivingportion 6016, a photoelectric element that receives light emitted fromthe light-emitting portion 6015 and converts it into an electric signalcan be used. A photodiode that can receive infrared rays can be suitablyused.

With the use of the light guide portion 6017 a and the light guideportion 6017 b which transmit the light 6018, the light-emitting portion6015 and the light-receiving portion 6016 can be placed under thedisplay device 6006, and a malfunction of the touch sensor due toexternal light reaching the light-receiving portion 6016 can beinhibited. Particularly when a resin that absorbs visible light andtransmits infrared rays is used, a malfunction of the touch sensor canbe inhibited more effectively.

At least part of this embodiment can be implemented in combination withthe other embodiments described in this specification as appropriate.

Embodiment 6

In this embodiment, examples of an electronic device for which thedisplay device of one embodiment of the present invention can be usedare described.

An electronic device 6500 illustrated in FIG. 18A is a portableinformation terminal that can be used as a smartphone.

The electronic device 6500 includes a housing 6501, a display portion6502, a power button 6503, buttons 6504, a speaker 6505, a microphone6506, a camera 6507, a light source 6508, and the like. The displayportion 6502 has a touch panel function.

The display device of one embodiment of the present invention can beused in the display portion 6502.

The display portion 6502 has a notch, and the camera 6507 and the lightsource 6508 are provided to be engaged with the notch. With such astructure, an area occupied by the display portion 6502 with respect tothe housing 6501 can be large.

Moreover, FIG. 18B shows an example in which the display portion 6502has an opening, and the camera 6507 and an annular light source 6509surrounding the camera 6507 are placed in the opening. Furthermore, thespeaker 6505 is provided to be engaged with the notch of the displayportion 6502. The display portion 6502 may be used as a light sourcethat illuminates a subject. With such a structure, an area occupied bythe display portion 6502 with respect to the housing 6501 can be large.

FIG. 18C is a schematic cross-sectional view including an end portion ofthe housing 6501 on the microphone 6506 side.

A protective member 6510 having a light-transmitting property isprovided on the display surface side of the housing 6501, and a displaypanel 6511, an optical member 6512, a touch sensor panel 6513, a printedcircuit board 6517, a battery 6518, and the like are provided in a spacesurrounded by the housing 6501 and the protective member 6510.

The display panel 6511, the optical member 6512, and the touch sensorpanel 6513 are fixed to the protective member 6510 with a bonding layernot illustrated.

Part of the display panel 6511 is bent in a region outside the displayportion 6502. An FPC 6515 is connected to the bent part. An IC 6516 ismounted on the FPC 6515. The FPC 6515 is connected to a terminalprovided for the printed circuit board 6517.

A flexible display panel of one embodiment of the present invention canbe used as the display panel 6511. Thus, an extremely lightweightelectronic device can be achieved. Furthermore, since the display panel6511 is extremely thin, the battery 6518 with a high capacity can beprovided without an increase in the thickness of the electronic device.Moreover, part of the display panel 6511 is bent to provide a connectionportion with the FPC 6515 on the back side of the pixel portion, wherebyan electronic device with a narrow bezel can be obtained.

At least part of this embodiment can be implemented in combination withthe other embodiments described in this specification as appropriate.

Embodiment 7

In this embodiment, electronic devices each including a display devicemanufactured using one embodiment of the present invention aredescribed.

Electronic devices exemplified below include a display device of oneembodiment of the present invention in a display portion. Thus, theelectronic devices achieve high resolution. In addition, the electronicdevices can achieve both high resolution and a large screen.

The display portion of the electronic device of one embodiment of thepresent invention can display an image with a resolution of, forexample, full high definition, 4K2K, 8K4K, 16K8K, or higher.

Examples of the electronic devices include a digital camera, a digitalvideo camera, a digital photo frame, a mobile phone, a portable gameconsole, a portable information terminal, and an audio reproducingdevice, in addition to electronic devices with a relatively largescreen, such as a television device, a laptop personal computer, amonitor device, digital signage, a pachinko machine, or a game machine.

The electronic device using one embodiment of the present invention canbe incorporated along a flat surface or a curved surface of an insidewall or an outside wall of a house or a building, an interior or anexterior of a car, or the like.

FIG. 19A is a diagram showing appearance of a camera 8000 to which afinder 8100 is attached.

The camera 8000 includes a housing 8001, a display portion 8002,operation buttons 8003, a shutter button 8004, and the like. Adetachable lens 8006 is attached to the camera 8000.

Note that the lens 8006 and the housing may be integrated with eachother in the camera 8000.

The camera 8000 can take images by the press of the shutter button 8004or touch on the display portion 8002 serving as a touch panel.

The housing 8001 includes a mount including an electrode, so that, inaddition to the finder 8100, a stroboscope or the like can be connectedto the housing.

The finder 8100 includes a housing 8101, a display portion 8102, abutton 8103, and the like.

The housing 8101 is attached to the camera 8000 with a mount engagingwith a mount of the camera 8000. The finder 8100 can display an image orthe like received from the camera 8000 on the display portion 8102.

The button 8103 serves as a power button or the like.

The display portion 8002 of the camera 8000 and the display portion 8102of the finder 8100 can use the display device of one embodiment of thepresent invention. Note that a finder may be incorporated in the camera8000.

FIG. 19B is a diagram showing appearance of a head-mounted display 8200.

The head-mounted display 8200 includes a mounting portion 8201, a lens8202, a main body 8203, a display portion 8204, a cable 8205, and thelike. A battery 8206 is incorporated in the mounting portion 8201.

The cable 8205 supplies electric power from the battery 8206 to the mainbody 8203. The main body 8203 includes a wireless receiver or the likeand can display received image data on the display portion 8204. Themain body 8203 is provided with a camera, and data on the movement ofthe user's eyeball and eyelid can be used as an input means.

The mounting portion 8201 may include a plurality of electrodes capableof sensing current flowing in response to the movement of the user'seyeball in a position in contact with the user to achieve a function ofrecognizing the user's sight line. A function of monitoring the user'spulse with the use of current flowing through the electrodes may beachieved. The mounting portion 8201 may include various sensors such asa temperature sensor, a pressure sensor, and an acceleration sensor tohave a function of displaying the user's biological information on thedisplay portion 8204 or a function of changing an image displayed on thedisplay portion 8204 in accordance with the movement of the user's head.

The display portion 8204 can use the display device of one embodiment ofthe present invention.

FIG. 19C, FIG. 19D, and FIG. 19E are diagrams showing appearance of ahead-mounted display 8300. The head-mounted display 8300 includes ahousing 8301, a display portion 8302, a band-shaped fixing unit 8304,and a pair of lenses 8305.

A user can see display on the display portion 8302 through the lenses8305. Note that the display portion 8302 is preferably curved andplaced, in which case the user can feel a high realistic sensation. Whenanother image displayed in a different region of the display portion8302 is viewed through the lenses 8305, three-dimensional display usingparallax or the like can also be performed. Note that the configurationis not limited to that in which one display portion 8302 is provided,and two display portions 8302 may be provided so that one displayportion is provided for one eye of the user.

Note that the display device of one embodiment of the present inventioncan be used in the display portion 8302. The display device includingthe semiconductor device of one embodiment of the present invention hasan extremely high resolution; thus, even when an image is magnifiedusing the lenses 8305 as in FIG. 19E, the user does not perceive pixels,and a more realistic image can be displayed.

Electronic devices illustrated in FIG. 20A to FIG. 20G include a housing9000, a display portion 9001, a speaker 9003, an operation key 9005(including a power switch or an operation switch), a connection terminal9006, a sensor 9007 (a sensor having a function of measuring force,displacement, position, speed, acceleration, angular velocity,rotational frequency, distance, light, liquid, magnetism, temperature, achemical substance, sound, time, hardness, electric field, current,voltage, electric power, radiation, flow rate, humidity, gradient,oscillation, a smell, or infrared rays), a microphone 9008, and thelike.

The electronic devices illustrated in FIG. 20A to FIG. 20G have avariety of functions. For example, the electronic devices can have afunction of displaying a variety of data (a still image, a moving image,a text image, and the like) on the display portion, a touch panelfunction, a function of displaying a calendar, date, time, and the like,a function of controlling processing with the use of a variety ofsoftware (programs), a wireless communication function, and a functionof reading out and processing a program or data stored in a recordingmedium. Note that the functions of the electronic devices are notlimited thereto, and the electronic devices can have a variety offunctions. The electronic devices may include a plurality of displayportions. The electronic devices may each include a camera or the likeand have a function of taking a still image or a moving image andstoring the taken image in a recording medium (external or incorporatedin the camera), a function of displaying the taken image on the displayportion, or the like.

The details of the electronic devices illustrated in FIG. 20A to FIG.20G are described below.

FIG. 20A is a perspective view showing a television device 9100. Thetelevision device 9100 can include the display portion 9001 having alarge screen size of, for example, 50 inches or more, or 100 inches ormore.

FIG. 20B is a perspective view showing a portable information terminal9101. For example, the portable information terminal 9101 can be used asa smartphone. Note that the portable information terminal 9101 may beprovided with the speaker 9003, the connection terminal 9006, the sensor9007, or the like. The portable information terminal 9101 can displaycharacters and image information on its plurality of surfaces. FIG. 20Bshows an example in which three icons 9050 are displayed. Information9051 indicated by dashed rectangles can be displayed on another surfaceof the display portion 9001. Examples of the information 9051 includenotification of reception of an e-mail, SNS, or an incoming call, thetitle and sender of an e-mail, SNS, or the like, the date, the time,remaining battery, and the reception strength of an antenna.Alternatively, the icon 9050 or the like may be displayed in theposition where the information 9051 is displayed.

FIG. 20C is a perspective view showing a portable information terminal9102. The portable information terminal 9102 has a function ofdisplaying information on three or more surfaces of the display portion9001. Here, an example in which information 9052, information 9053, andinformation 9054 are displayed on different surfaces is shown. Forexample, a user can check the information 9053 displayed in a positionthat can be observed from above the portable information terminal 9102,with the portable information terminal 9102 put in a breast pocket ofhis/her clothes. The user can see the display without taking out theportable information terminal 9102 from the pocket and decide whether toanswer the call, for example.

FIG. 20D is a perspective view showing a watch-type portable informationterminal 9200. For example, the portable information terminal 9200 canbe used as a smart watch. The display surface of the display portion9001 is curved and provided, and display can be performed along thecurved display surface. Mutual communication between the portableinformation terminal 9200 and, for example, a headset capable ofwireless communication enables hands-free calling. With the connectionterminal 9006, the portable information terminal 9200 can perform mutualdata transmission with another information terminal and charging. Notethat the charging operation may be performed by wireless power feeding.

FIG. 20E, FIG. 20F, and FIG. 20G are perspective views showing afoldable portable information terminal 9201. FIG. 20E is a perspectiveview of an opened state of the portable information terminal 9201, FIG.20G is a perspective view of a folded state thereof, and FIG. 20F is aperspective view of a state in the middle of change from one of FIG. 20Eand FIG. 20G to the other. The portable information terminal 9201 ishighly portable in the folded state and is highly browsable in theopened state because of a seamless large display region. The displayportion 9001 of the portable information terminal 9201 is supported bythree housings 9000 joined by hinges 9055. For example, the displayportion 9001 can be folded with a radius of curvature of greater than orequal to 1 mm and less than or equal to 150 mm.

FIG. 21A shows an example of a television device. In a television device7100, a display portion 7500 is incorporated in a housing 7101. Here, astructure in which the housing 7101 is supported by a stand 7103 isillustrated.

Operation of the television device 7100 illustrated in FIG. 21A can beperformed with an operation switch provided in the housing 7101 or aseparate remote controller 7111. Alternatively, a touch panel may beused for the display portion 7500, and the television device 7100 may beoperated by touch on the touch panel. The remote controller 7111 may beprovided with a display portion in addition to operation buttons.

Note that the television device 7100 may include a television receiverand a communication device for a network connection.

FIG. 21B illustrates a laptop personal computer 7200. The laptoppersonal computer 7200 includes a housing 7211, a keyboard 7212, apointing device 7213, an external connection port 7214, and the like. Inthe housing 7211, the display portion 7500 is incorporated.

FIG. 21C and FIG. 21D show examples of digital signage.

Digital signage 7300 illustrated in FIG. 21C includes a housing 7301,the display portion 7500, a speaker 7303, and the like. Furthermore, thedigital signage can include an LED lamp, operation keys (including apower switch or an operation switch), a connection terminal, a varietyof sensors, a microphone, and the like.

FIG. 21D illustrates digital signage 7400 attached to a cylindricalpillar 7401. The digital signage 7400 includes the display portion 7500provided along a curved surface of the pillar 7401.

The larger display portion 7500 can increase the amount of data that canbe provided at a time and attracts more attention, so that theeffectiveness of the advertisement can be increased, for example.

A touch panel is preferably used in the display portion 7500 so that theuser can operate the digital signage. Thus, the digital signage can beused for not only advertising but also providing information that theuser needs, such as route information, traffic information, and aninformation map of a commercial facility.

As illustrated in FIG. 21C and FIG. 21D, it is preferable that thedigital signage 7300 or the digital signage 7400 be capable of workingwith an information terminal 7311 such as user's smartphone throughwireless communication. For example, information of an advertisementdisplayed on the display portion 7500 can be displayed on a screen ofthe information terminal 7311. By operation of the information terminal7311, display on the display portion 7500 can be switched.

It is possible to make the digital signage 7300 or the digital signage7400 execute a game with the use of the information terminal 7311 as anoperation means (controller). Thus, an unspecified number of users canjoin in and enjoy the game concurrently.

The display device of one embodiment of the present invention can beused in the display portion 7500 in FIG. 21A to FIG. 21D.

The electronic devices of this embodiment each include a displayportion; however, one embodiment of the present invention can also beused in an electronic device without a display portion.

REFERENCE NUMERALS

10, 10 a, 10 b: display device, 11: display portion, 12, 12 a, 12 b:connection terminal, 13, 14, 14 a, 14 p, 14 q, 15, 15 a : wiring, 13 a,13 b, 13 d: opening, 13 c: intersecting portion, 14 b: processing trace,16: FPC, 17: connector, 18: connection portion, 19: IC, 20 a, 20 b, 20c: cut line, 21, 21 a, 22: substrate, 25: bonding layer, 30, 30 a, 30 b,30 c, 30 d, 40, 40 a, 40 b: transistor, 31: semiconductor layer, 32, 32p, 35, 35 p, 36, 36 p, 37, 38, 38 p, 39: conductive layer, 33, 41, 42,43, 45, 46: insulating layer, 34: low-resistance region, 50 a, 50 b:bent portion, 51: substrate, 52, 53: circuit portion, 54: notch, 100 a,100 b, 100 c, 100 d, 100 e: TEG, 101: element to be measured, 102:terminal, 103: wiring, 120: cut line, 701, 705: substrate, 710: liquidcrystal element, 711, 713: conductive layer, 712: liquid crystal, 720:support, 721, 722, 750, 752: transistor, 723: wiring, 725, 726:alignment film, 727: spacer, 730, 734, 741 a, 741 b, 741 c, 744, 746,770: insulating layer, 732: sealing layer, 736: coloring layer, 738:light-blocking layer, 740: substrate, 741: protective layer, 742, 747,748: bonding layer, 743: resin layer, 749: protective layer, 755, 756:polarizing plate, 757: light source, 761, 772, 788: conductive layer,782: light-emitting element, 786: EL layer, 790: capacitor

What is claimed is:
 1. A display device comprising a substrate, a display portion, a first wiring, and a second wiring, wherein the display portion comprises a transistor, wherein the transistor comprises a semiconductor layer, a gate insulating layer, and a gate electrode, wherein the semiconductor layer at least comprises one metal element that is the same as the metal element included in the second wiring, wherein the semiconductor layer comprises a first region overlapping with the gate electrode and a second region not overlapping with the gate electrode, and wherein a resistance of the second region and a resistance of the second wiring are lower than a resistance of the first region.
 2. A display device comprising a substrate, a display portion, a first wiring, and a second wiring, wherein the display portion comprises a transistor, wherein the transistor comprises a semiconductor layer, a gate insulating layer, and a gate electrode, wherein the semiconductor layer and the second wiring comprise the same metal oxide, wherein the semiconductor layer comprises a first region overlapping with the gate electrode and a second region not overlapping with the gate electrode, and wherein a resistance of the second region and a resistance of the second wiring are lower than a resistance of the first region.
 3. The display device according to claim 1, wherein the semiconductor layer and the second wiring are provided on the same plane.
 4. The display device according to claim 2, wherein the semiconductor layer and the second wiring are provided on the same plane.
 5. The display device according to claim 1, wherein the resistance of the second wiring is higher than a resistance of the first wiring.
 6. The display device according to claim 2, wherein the resistance of the second wiring is higher than a resistance of the first wiring.
 7. The display device according to claim 1, further comprising: a third wiring electrically connected to the transistor, wherein the third wiring and the first wiring are provided on the same plane and comprise the same metal element.
 8. The display device according to claim 2, further comprising: a third wiring electrically connected to the transistor, wherein the third wiring and the first wiring are provided on the same plane and comprise the same metal element.
 9. The display device according to claim 1, further comprising an FPC, wherein the FPC comprises a portion covering an exposed end surface of the second wiring.
 10. The display device according to claim 2, further comprising an FPC, wherein the FPC comprises a portion covering an exposed end surface of the second wiring.
 11. A method for manufacturing a display device comprising the steps of: forming a transistor comprising a semiconductor layer over a substrate; and forming a wiring over the substrate; wherein the semiconductor layer and the wiring are formed by processing the same metal oxide film, wherein the semiconductor layer comprises a first region overlapping with a gate electrode and a second region not overlapping with the gate electrode, and wherein a resistance of the second region and a resistance of the wiring are lower than a resistance of the first region.
 12. The method for manufacturing a display device according to claim 11, further comprising the steps of: forming a plurality of connection terminals over the substrate; cutting part of the substrate and part of the wiring to isolate the plurality of connection terminals electrically; and connecting an FPC to the plurality of connection terminals.
 13. The method for manufacturing a display device according to claim 12, wherein the FPC comprises a portion covering an exposed end surface of the wiring.
 14. The method for manufacturing a display device according to claim 11, wherein the semiconductor layer and the wiring are provided on the same plane. 